attack each other and backroom block

gradle.properties

@@ -6,7 +6,7 @@ minecraft_version=1.20.1
 yarn_mappings=1.20.1+build.10
 loader_version=0.18.3
 # Mod Properties
-mod_version=26.3.16.1
+mod_version=26.3.17
 maven_group=dev.tggamesyt
 archives_base_name=szar
 # Dependencies

src/main/java/dev/tggamesyt/szar/AttackEnemyTeamGoal.java

@@ -0,0 +1,18 @@
+// AttackEnemyTeamGoal.java
+package dev.tggamesyt.szar;
+
+import net.minecraft.entity.LivingEntity;
+import net.minecraft.entity.ai.goal.ActiveTargetGoal;
+import net.minecraft.entity.mob.PathAwareEntity;
+
+public class AttackEnemyTeamGoal extends ActiveTargetGoal<LivingEntity> {
+
+    public AttackEnemyTeamGoal(PathAwareEntity mob, String myTeam) {
+        super(mob, LivingEntity.class, true, target -> {
+            if (target instanceof TeamMember other) {
+                return !other.getTeam().equals(myTeam);
+            }
+            return false;
+        });
+    }
+}

src/main/java/dev/tggamesyt/szar/CommunistEntity.java

@@ -1,7 +1,9 @@
 package dev.tggamesyt.szar;
 
+import net.minecraft.entity.EntityData;
 import net.minecraft.entity.EntityType;
 import net.minecraft.entity.EquipmentSlot;
+import net.minecraft.entity.SpawnReason;
 import net.minecraft.entity.ai.goal.WanderAroundFarGoal;
 import net.minecraft.entity.attribute.DefaultAttributeContainer;
 import net.minecraft.entity.attribute.EntityAttributes;
@@ -13,10 +15,13 @@ import net.minecraft.item.Items;
 import net.minecraft.nbt.NbtCompound;
 import net.minecraft.nbt.NbtList;
 import net.minecraft.nbt.NbtString;
+import net.minecraft.server.world.ServerWorld;
+import net.minecraft.world.LocalDifficulty;
+import net.minecraft.world.ServerWorldAccess;
 import net.minecraft.world.World;
 import org.jetbrains.annotations.Nullable;
 
-public class CommunistEntity extends PathAwareEntity implements Arrestable{
+public class CommunistEntity extends PathAwareEntity implements Arrestable, TeamMember {
 
     public static boolean arrestable = false;
     @Nullable
@@ -31,6 +36,9 @@ public class CommunistEntity extends PathAwareEntity implements Arrestable{
         this.goalSelector.add(2, new FollowLeaderWanderGoal(this, 1.0D, 6.0F));
         this.goalSelector.add(3, new WanderAroundFarGoal(this, 0.8D));
         this.goalSelector.add(1, new AK47AttackGoal(this, 16.0F, 2));
+
+        this.targetSelector.add(1, new AggroOnHitRevengeGoal(this));
+        this.targetSelector.add(2, new AttackEnemyTeamGoal(this, "communist"));
     }
 
 
@@ -85,5 +93,41 @@ public class CommunistEntity extends PathAwareEntity implements Arrestable{
     public StalinEntity getLeader() {
         return this.leader;
     }
+    @Override
+    public String getTeam() {
+        return "communist";
+    }
 
+    @Override
+    @Nullable
+    public EntityData initialize(
+            ServerWorldAccess world,
+            LocalDifficulty difficulty,
+            SpawnReason spawnReason,
+            @Nullable EntityData entityData,
+            @Nullable NbtCompound entityNbt
+    ) {
+        EntityData data = super.initialize(world, difficulty, spawnReason, entityData, entityNbt);
+
+        // Only auto-assign if NOT spawned as part of Stalin's group
+        // (Stalin's group sets the leader manually after this call)
+        if (this.leader == null && world instanceof ServerWorld serverWorld) {
+            StalinEntity nearest = serverWorld.getEntitiesByClass(
+                            StalinEntity.class,
+                            this.getBoundingBox().expand(24),
+                            s -> s.isAlive()
+                    ).stream()
+                    .min((a, b) -> Double.compare(
+                            a.squaredDistanceTo(this),
+                            b.squaredDistanceTo(this)
+                    ))
+                    .orElse(null);
+
+            if (nearest != null) {
+                this.setLeader(nearest);
+            }
+        }
+
+        return data;
+    }
 }

src/main/java/dev/tggamesyt/szar/HitterEntity.java

@@ -25,7 +25,7 @@ import java.util.List;
 
 import static dev.tggamesyt.szar.Szar.NaziEntityType;
 
-public class HitterEntity extends PathAwareEntity implements Arrestable{
+public class HitterEntity extends PathAwareEntity implements Arrestable, TeamMember {
 
     public static boolean arrestable = true;
 
@@ -40,6 +40,7 @@ public class HitterEntity extends PathAwareEntity implements Arrestable{
         this.goalSelector.add(3, new LookAroundGoal(this));
 
         this.targetSelector.add(1, new AggroOnHitRevengeGoal(this));
+        this.targetSelector.add(2, new AttackEnemyTeamGoal(this, "nazi"));
     }
 
 
@@ -146,5 +147,8 @@ public class HitterEntity extends PathAwareEntity implements Arrestable{
         }
     }
 
-
+    @Override
+    public String getTeam() {
+        return "nazi";
+    }
 }

src/main/java/dev/tggamesyt/szar/NaziEntity.java

@@ -1,7 +1,9 @@
 package dev.tggamesyt.szar;
 
+import net.minecraft.entity.EntityData;
 import net.minecraft.entity.EntityType;
 import net.minecraft.entity.EquipmentSlot;
+import net.minecraft.entity.SpawnReason;
 import net.minecraft.entity.ai.goal.WanderAroundFarGoal;
 import net.minecraft.entity.attribute.DefaultAttributeContainer;
 import net.minecraft.entity.attribute.EntityAttributes;
@@ -13,10 +15,13 @@ import net.minecraft.item.Items;
 import net.minecraft.nbt.NbtCompound;
 import net.minecraft.nbt.NbtList;
 import net.minecraft.nbt.NbtString;
+import net.minecraft.server.world.ServerWorld;
+import net.minecraft.world.LocalDifficulty;
+import net.minecraft.world.ServerWorldAccess;
 import net.minecraft.world.World;
 import org.jetbrains.annotations.Nullable;
 
-public class NaziEntity extends PathAwareEntity implements Arrestable{
+public class NaziEntity extends PathAwareEntity implements Arrestable, TeamMember {
 
     private boolean hithandPlaying = false;
     private int hithandTimer = 0; // ticks remaining
@@ -84,6 +89,9 @@ public class NaziEntity extends PathAwareEntity implements Arrestable{
         this.goalSelector.add(2, new FollowLeaderWanderGoal(this, 1.0D, 6.0F));
         this.goalSelector.add(3, new WanderAroundFarGoal(this, 0.8D));
         this.goalSelector.add(1, new AK47AttackGoal(this, 16.0F, 2));
+
+        this.targetSelector.add(1, new AggroOnHitRevengeGoal(this));
+        this.targetSelector.add(2, new AttackEnemyTeamGoal(this, "nazi"));
     }
 
 
@@ -138,5 +146,41 @@ public class NaziEntity extends PathAwareEntity implements Arrestable{
     public HitterEntity getLeader() {
         return this.leader;
     }
+    @Override
+    public String getTeam() {
+        return "nazi";
+    }
 
+    @Override
+    @Nullable
+    public EntityData initialize(
+            ServerWorldAccess world,
+            LocalDifficulty difficulty,
+            SpawnReason spawnReason,
+            @Nullable EntityData entityData,
+            @Nullable NbtCompound entityNbt
+    ) {
+        EntityData data = super.initialize(world, difficulty, spawnReason, entityData, entityNbt);
+
+        // Only auto-assign if NOT spawned as part of Stalin's group
+        // (Stalin's group sets the leader manually after this call)
+        if (this.leader == null && world instanceof ServerWorld serverWorld) {
+            HitterEntity nearest = serverWorld.getEntitiesByClass(
+                            HitterEntity.class,
+                            this.getBoundingBox().expand(24),
+                            s -> s.isAlive()
+                    ).stream()
+                    .min((a, b) -> Double.compare(
+                            a.squaredDistanceTo(this),
+                            b.squaredDistanceTo(this)
+                    ))
+                    .orElse(null);
+
+            if (nearest != null) {
+                this.setLeader(nearest);
+            }
+        }
+
+        return data;
+    }
 }

src/main/java/dev/tggamesyt/szar/PortalBlock.java

@@ -0,0 +1,252 @@
+package dev.tggamesyt.szar;
+
+import net.minecraft.block.Block;
+import net.minecraft.block.BlockState;
+import net.minecraft.block.ShapeContext;
+import net.minecraft.entity.Entity;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.entity.player.PlayerInventory;
+import net.minecraft.item.ItemStack;
+import net.minecraft.nbt.NbtCompound;
+import net.minecraft.nbt.NbtList;
+import net.minecraft.registry.RegistryKey;
+import net.minecraft.registry.RegistryKeys;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.network.ServerPlayerEntity;
+import net.minecraft.server.world.ServerWorld;
+import net.minecraft.util.Identifier;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.shape.VoxelShape;
+import net.minecraft.util.shape.VoxelShapes;
+import net.minecraft.world.World;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class PortalBlock extends Block {
+
+    // Cooldown tracker so players don't teleport 20x per second
+    private static final java.util.Map<java.util.UUID, Long> cooldowns = new java.util.HashMap<>();
+
+    public PortalBlock(Settings settings) {
+        super(settings);
+    }
+
+    @Override
+    public VoxelShape getCollisionShape(BlockState state, net.minecraft.world.BlockView world,
+                                        BlockPos pos, ShapeContext ctx) {
+        return VoxelShapes.empty();
+    }
+
+    @Override
+    public void onEntityCollision(BlockState state, World world, BlockPos pos,
+                                  Entity entity) {
+        if (world.isClient) return;
+        if (!(entity instanceof ServerPlayerEntity player)) return;
+
+        // Cooldown check — 3 seconds
+        long now = world.getTime();
+        Long last = cooldowns.get(player.getUuid());
+        if (last != null && now - last < 60) return;
+        cooldowns.put(player.getUuid(), now);
+
+        // Find the TrackerBlock above (within 5 blocks)
+        TrackerBlockEntity tracker = findTrackerAbove(world, pos);
+        if (tracker == null) return;
+
+        MinecraftServer server = world.getServer();
+        if (server == null) return;
+
+        if (!tracker.isNetherSide) {
+            // --- OVERWORLD → NETHER ---
+            teleportToNether(player, tracker, server, pos);
+        } else {
+            // --- NETHER → OVERWORLD ---
+            teleportToOverworld(player, tracker, server);
+        }
+    }
+
+    private void teleportToNether(ServerPlayerEntity player, TrackerBlockEntity tracker,
+                                  MinecraftServer server, BlockPos portalPos) {
+        // Save return position (a few blocks above entry)
+        tracker.returnX = player.getX();
+        tracker.returnY = player.getY() + 3;
+        tracker.returnZ = player.getZ();
+        tracker.markDirty();
+
+        // Save inventory
+        NbtList savedInventory = saveInventory(player);
+
+        // Clear inventory
+        player.getInventory().clear();
+
+        // Register player as inside
+        tracker.addPlayer(player.getUuid());
+
+        // Teleport to nether
+        ServerWorld nether = server.getWorld(World.NETHER);
+        if (nether == null) return;
+
+        double netherX = player.getX();
+        double netherZ = player.getZ();
+        double netherY = findSafeY(nether, (int) netherX, (int) netherZ);
+
+        // Store saved inventory in player's persistent data
+        NbtCompound persistent = player.writeNbt(new NbtCompound());
+        // We use a custom data attachment via the player's nbt
+        saveInventoryToPlayer(player, savedInventory);
+
+        // Store which overworld tracker owns this player
+        NbtCompound tag = getOrCreateCustomData(player);
+        tag.putInt("OwnerTrackerX", tracker.getPos().getX());
+        tag.putInt("OwnerTrackerY", tracker.getPos().getY());
+        tag.putInt("OwnerTrackerZ", tracker.getPos().getZ());
+
+        // Generate nether-side portal structure
+        BlockPos netherPortalPos = new BlockPos((int) netherX, (int) netherY, (int) netherZ);
+        generateNetherPortal(nether, netherPortalPos, tracker);
+
+        // Teleport
+        player.teleport(nether, netherX, netherY + 1, netherZ,
+                player.getYaw(), player.getPitch());
+    }
+
+    private void teleportToOverworld(ServerPlayerEntity player, TrackerBlockEntity tracker,
+                                     MinecraftServer server) {
+        // Restore inventory
+        restoreInventoryToPlayer(player);
+
+        // Remove from nether tracker
+        tracker.removePlayer(player.getUuid());
+
+        // Find overworld paired tracker and remove from that too
+        ServerWorld overworld = server.getWorld(World.OVERWORLD);
+        if (overworld != null && tracker.pairedTrackerPos != null) {
+            if (overworld.getBlockEntity(tracker.pairedTrackerPos)
+                    instanceof TrackerBlockEntity owTracker) {
+                owTracker.removePlayer(player.getUuid());
+
+                // If no players left, remove both trackers and their portal blocks
+                if (!owTracker.hasPlayers()) {
+                    removePortalStructure(overworld, tracker.pairedTrackerPos);
+                    removePortalStructure((ServerWorld) player.getWorld(), tracker.getPos());
+                }
+            }
+        }
+
+        // Teleport back (a few blocks above entry)
+        player.teleport(overworld,
+                tracker.returnX, tracker.returnY, tracker.returnZ,
+                player.getYaw(), player.getPitch());
+    }
+
+    // --- Helpers ---
+
+    private TrackerBlockEntity findTrackerAbove(World world, BlockPos portalPos) {
+        for (int i = 1; i <= 5; i++) {
+            BlockPos check = portalPos.up(i);
+            if (world.getBlockState(check).getBlock() instanceof TrackerBlock) {
+                if (world.getBlockEntity(check) instanceof TrackerBlockEntity te) {
+                    return te;
+                }
+            }
+        }
+        return null;
+    }
+
+    private double findSafeY(ServerWorld world, int x, int z) {
+        // Search from y=100 downward for solid ground with 2 air blocks above
+        for (int y = 100; y > 10; y--) {
+            BlockPos feet = new BlockPos(x, y, z);
+            BlockPos head = feet.up();
+            BlockPos ground = feet.down();
+            if (!world.getBlockState(feet).isSolidBlock(world, feet)
+                    && !world.getBlockState(head).isSolidBlock(world, head)
+                    && world.getBlockState(ground).isSolidBlock(world, ground)) {
+                return y;
+            }
+        }
+        return 64; // fallback
+    }
+
+    private void generateNetherPortal(ServerWorld nether, BlockPos portalPos,
+                                      TrackerBlockEntity overworldTracker) {
+        // Place TrackerBlock 4 blocks above portal
+        BlockPos trackerPos = portalPos.up(4);
+        nether.setBlockState(trackerPos, Szar.TRACKER_BLOCK.getDefaultState());
+
+        if (nether.getBlockEntity(trackerPos) instanceof TrackerBlockEntity netherTracker) {
+            netherTracker.isNetherSide = true;
+            netherTracker.returnX = overworldTracker.returnX;
+            netherTracker.returnY = overworldTracker.returnY;
+            netherTracker.returnZ = overworldTracker.returnZ;
+            netherTracker.pairedTrackerPos = overworldTracker.getPos();
+            overworldTracker.pairedTrackerPos = trackerPos;
+            overworldTracker.markDirty();
+            netherTracker.markDirty();
+        }
+
+        // Place portal block at bottom
+        nether.setBlockState(portalPos, Szar.PORTAL_BLOCK.getDefaultState());
+    }
+
+    private void removePortalStructure(ServerWorld world, BlockPos trackerPos) {
+        // Remove tracker
+        world.removeBlock(trackerPos, false);
+        // Remove portal block (4 below)
+        world.removeBlock(trackerPos.down(4), false);
+    }
+
+    // Inventory persistence via player NBT custom data
+    private static final String INV_KEY = "SzarSavedInventory";
+
+    private NbtList saveInventory(ServerPlayerEntity player) {
+        NbtList list = new NbtList();
+        PlayerInventory inv = player.getInventory();
+        for (int i = 0; i < inv.size(); i++) {
+            ItemStack stack = inv.getStack(i);
+            if (!stack.isEmpty()) {
+                NbtCompound entry = new NbtCompound();
+                entry.putInt("Slot", i);
+                stack.writeNbt(entry);
+                list.add(entry);
+            }
+        }
+        return list;
+    }
+
+    private void saveInventoryToPlayer(ServerPlayerEntity player, NbtList inventory) {
+        NbtCompound tag = getOrCreateCustomData(player);
+        tag.put(INV_KEY, inventory);
+    }
+
+    private void restoreInventoryToPlayer(ServerPlayerEntity player) {
+        NbtCompound tag = getOrCreateCustomData(player);
+        if (!tag.contains(INV_KEY)) return;
+
+        NbtList list = tag.getList(INV_KEY, 10); // 10 = NbtCompound type
+        player.getInventory().clear();
+
+        for (int i = 0; i < list.size(); i++) {
+            NbtCompound entry = list.getCompound(i);
+            int slot = entry.getInt("Slot");
+            ItemStack stack = ItemStack.fromNbt(entry);
+            player.getInventory().setStack(slot, stack);
+        }
+
+        tag.remove(INV_KEY);
+    }
+
+    // Fabric doesn't have a built-in persistent custom data on players in 1.20.1
+    // without a mod like FAPI's PersistentStateManager trick.
+    // The cleanest approach in vanilla Fabric is to store it in a custom
+    // ServerState attached to the overworld.
+    private NbtCompound getOrCreateCustomData(ServerPlayerEntity player) {
+        // We'll use the player's existing nbt stack — store in a sub-tag
+        // This works for the session but won't survive a crash mid-dimension.
+        // For a robust solution, use a PersistentState (shown below in PortalDataState.java)
+        return PortalDataState.getOrCreate(
+                player.getServer().getWorld(World.OVERWORLD)
+        ).getOrCreatePlayerData(player.getUuid());
+    }
+}

src/main/java/dev/tggamesyt/szar/PortalDataState.java

@@ -0,0 +1,46 @@
+package dev.tggamesyt.szar;
+
+import net.minecraft.nbt.NbtCompound;
+import net.minecraft.server.world.ServerWorld;
+import net.minecraft.world.PersistentState;
+
+import java.util.UUID;
+
+public class PortalDataState extends PersistentState {
+
+    private static final String KEY = "szar_portal_data";
+    private final NbtCompound data = new NbtCompound();
+
+    public NbtCompound getOrCreatePlayerData(UUID uuid) {
+        String key = uuid.toString();
+        if (!data.contains(key)) {
+            data.put(key, new NbtCompound());
+        }
+        return data.getCompound(key);
+    }
+
+    public void removePlayerData(UUID uuid) {
+        data.remove(uuid.toString());
+        markDirty();
+    }
+
+    @Override
+    public NbtCompound writeNbt(NbtCompound nbt) {
+        nbt.put("PlayerData", data.copy());
+        return nbt;
+    }
+
+    public static PortalDataState fromNbt(NbtCompound nbt) {
+        PortalDataState state = new PortalDataState();
+        NbtCompound saved = nbt.getCompound("PlayerData");
+        for (String key : saved.getKeys()) {
+            state.data.put(key, saved.getCompound(key));
+        }
+        return state;
+    }
+
+    public static PortalDataState getOrCreate(ServerWorld overworld) {
+        return overworld.getPersistentStateManager()
+                .getOrCreate(PortalDataState::fromNbt, PortalDataState::new, KEY);
+    }
+}

src/main/java/dev/tggamesyt/szar/StalinEntity.java

@@ -26,7 +26,7 @@ import java.util.List;
 
 import static dev.tggamesyt.szar.Szar.CommunistEntityType;
 
-public class StalinEntity extends PathAwareEntity implements Arrestable{
+public class StalinEntity extends PathAwareEntity implements Arrestable, TeamMember {
 
     public static boolean arrestable = true;
 
@@ -41,6 +41,7 @@ public class StalinEntity extends PathAwareEntity implements Arrestable{
         this.goalSelector.add(3, new LookAroundGoal(this));
 
         this.targetSelector.add(1, new AggroOnHitRevengeGoal(this));
+        this.targetSelector.add(2, new AttackEnemyTeamGoal(this, "communist"));
     }
 
 
@@ -148,4 +149,8 @@ public class StalinEntity extends PathAwareEntity implements Arrestable{
     }
 
 
+    @Override
+    public String getTeam() {
+        return "communist";
+    }
 }

src/main/java/dev/tggamesyt/szar/Szar.java

@@ -1065,6 +1065,38 @@ public class Szar implements ModInitializer {
             });
         });
     }
+    // Blocks
+    public static final TrackerBlock TRACKER_BLOCK = Registry.register(
+            Registries.BLOCK, new Identifier(MOD_ID, "tracker"),
+            new TrackerBlock(FabricBlockSettings.create().noCollision().air())
+            // .air() makes it not render and not block light
+    );
+
+    public static final PortalBlock PORTAL_BLOCK = Registry.register(
+            Registries.BLOCK, new Identifier(MOD_ID, "portal"),
+            new PortalBlock(FabricBlockSettings.create().noCollision()
+                    .strength(-1.0f) // indestructible by default, change if needed
+                    .luminance(state -> 11)) // slight glow so you can see it
+    );
+
+    // Block items (so you can place them)
+    public static final BlockItem TRACKER_BLOCK_ITEM = Registry.register(
+            Registries.ITEM, new Identifier(MOD_ID, "tracker"),
+            new BlockItem(TRACKER_BLOCK, new FabricItemSettings())
+    );
+
+    public static final BlockItem PORTAL_BLOCK_ITEM = Registry.register(
+            Registries.ITEM, new Identifier(MOD_ID, "portal"),
+            new BlockItem(PORTAL_BLOCK, new FabricItemSettings())
+    );
+
+    // Block entity
+    public static final BlockEntityType<TrackerBlockEntity> TRACKER_BLOCK_ENTITY =
+            Registry.register(
+                    Registries.BLOCK_ENTITY_TYPE,
+                    new Identifier(MOD_ID, "tracker"),
+                    FabricBlockEntityTypeBuilder.create(TrackerBlockEntity::new, TRACKER_BLOCK).build()
+            );
 
     // In your ModItems or wherever you register items
     public static final Item REVOLVER = Registry.register(

src/main/java/dev/tggamesyt/szar/TeamMember.java

@@ -0,0 +1,5 @@
+package dev.tggamesyt.szar;
+
+public interface TeamMember {
+    String getTeam(); // returns "communist" or "tsarist" (or whatever your 2nd team is)
+}

src/main/java/dev/tggamesyt/szar/TrackerBlock.java

@@ -0,0 +1,52 @@
+package dev.tggamesyt.szar;
+
+import net.minecraft.block.Block;
+import net.minecraft.block.BlockEntityProvider;
+import net.minecraft.block.BlockState;
+import net.minecraft.block.ShapeContext;
+import net.minecraft.block.entity.BlockEntity;
+import net.minecraft.entity.LivingEntity;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.item.ItemStack;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.shape.VoxelShape;
+import net.minecraft.util.shape.VoxelShapes;
+import net.minecraft.world.BlockView;
+import net.minecraft.world.World;
+import org.jetbrains.annotations.Nullable;
+
+public class TrackerBlock extends Block implements BlockEntityProvider {
+
+    public TrackerBlock(Settings settings) {
+        super(settings);
+    }
+
+    // No hitbox
+    @Override
+    public VoxelShape getOutlineShape(BlockState state, BlockView world,
+                                      BlockPos pos, ShapeContext ctx) {
+        return VoxelShapes.empty();
+    }
+
+    // No collision
+    @Override
+    public VoxelShape getCollisionShape(BlockState state, BlockView world,
+                                        BlockPos pos, ShapeContext ctx) {
+        return VoxelShapes.empty();
+    }
+
+    @Nullable
+    @Override
+    public BlockEntity createBlockEntity(BlockPos pos, BlockState state) {
+        return new TrackerBlockEntity(pos, state);
+    }
+
+    @Override
+    public void onPlaced(World world, BlockPos pos, BlockState state,
+                         @Nullable LivingEntity placer, ItemStack itemStack) {
+        if (world.isClient) return;
+
+        BlockPos portalPos = pos.down(4);
+        world.setBlockState(portalPos, Szar.PORTAL_BLOCK.getDefaultState());
+    }
+}

src/main/java/dev/tggamesyt/szar/TrackerBlockEntity.java

@@ -0,0 +1,91 @@
+package dev.tggamesyt.szar;
+
+import net.minecraft.block.BlockState;
+import net.minecraft.block.entity.BlockEntity;
+import net.minecraft.nbt.NbtCompound;
+import net.minecraft.nbt.NbtList;
+import net.minecraft.nbt.NbtString;
+import net.minecraft.util.math.BlockPos;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.UUID;
+
+public class TrackerBlockEntity extends BlockEntity {
+
+    // The overworld entry coords (used by nether-side tracker to know where to send players back)
+    public double returnX, returnY, returnZ;
+    // Whether this tracker is in the nether or overworld
+    public boolean isNetherSide = false;
+    // BlockPos of the paired tracker in the other dimension
+    public BlockPos pairedTrackerPos = null;
+
+    // UUIDs of players currently inside the dimension via this portal
+    private final Set<UUID> playersInside = new HashSet<>();
+
+    public TrackerBlockEntity(BlockPos pos, BlockState state) {
+        super(Szar.TRACKER_BLOCK_ENTITY, pos, state);
+    }
+
+    public void addPlayer(UUID uuid) {
+        playersInside.add(uuid);
+        markDirty();
+    }
+
+    public void removePlayer(UUID uuid) {
+        playersInside.remove(uuid);
+        markDirty();
+    }
+
+    public boolean hasPlayers() {
+        return !playersInside.isEmpty();
+    }
+
+    public Set<UUID> getPlayersInside() {
+        return playersInside;
+    }
+
+    @Override
+    public void writeNbt(NbtCompound nbt) {
+        super.writeNbt(nbt);
+        nbt.putDouble("ReturnX", returnX);
+        nbt.putDouble("ReturnY", returnY);
+        nbt.putDouble("ReturnZ", returnZ);
+        nbt.putBoolean("IsNetherSide", isNetherSide);
+
+        if (pairedTrackerPos != null) {
+            nbt.putInt("PairedX", pairedTrackerPos.getX());
+            nbt.putInt("PairedY", pairedTrackerPos.getY());
+            nbt.putInt("PairedZ", pairedTrackerPos.getZ());
+        }
+
+        NbtList list = new NbtList();
+        for (UUID uuid : playersInside) {
+            list.add(NbtString.of(uuid.toString()));
+        }
+        nbt.put("PlayersInside", list);
+    }
+
+    @Override
+    public void readNbt(NbtCompound nbt) {
+        super.readNbt(nbt);
+        returnX = nbt.getDouble("ReturnX");
+        returnY = nbt.getDouble("ReturnY");
+        returnZ = nbt.getDouble("ReturnZ");
+        isNetherSide = nbt.getBoolean("IsNetherSide");
+
+        if (nbt.contains("PairedX")) {
+            pairedTrackerPos = new BlockPos(
+                    nbt.getInt("PairedX"),
+                    nbt.getInt("PairedY"),
+                    nbt.getInt("PairedZ")
+            );
+        }
+
+        NbtList list = nbt.getList("PlayersInside", 8);
+        playersInside.clear();
+        for (int i = 0; i < list.size(); i++) {
+            playersInside.add(UUID.fromString(list.getString(i)));
+        }
+    }
+}

src/main/java/dev/tggamesyt/szar/mixin/NoClipMixin.java

@@ -0,0 +1,39 @@
+package dev.tggamesyt.szar.mixin;
+
+import dev.tggamesyt.szar.TrackerBlock;
+import net.minecraft.block.AbstractBlock;
+import net.minecraft.block.BlockState;
+import net.minecraft.block.ShapeContext;
+import net.minecraft.block.EntityShapeContext;
+import net.minecraft.entity.Entity;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.shape.VoxelShape;
+import net.minecraft.util.shape.VoxelShapes;
+import net.minecraft.world.BlockView;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(AbstractBlock.AbstractBlockState.class)
+public class NoClipMixin {
+
+    @Inject(method = "getCollisionShape*", at = @At("HEAD"), cancellable = true)
+    private void szar_noClipBelowTracker(BlockView world, BlockPos pos,
+                                         ShapeContext ctx, CallbackInfoReturnable<VoxelShape> cir) {
+        // Only applies to players
+        if (!(ctx instanceof EntityShapeContext esc)) return;
+        Entity entity = esc.getEntity();
+        if (!(entity instanceof PlayerEntity)) return;
+
+        // Check 1–5 blocks above this position for a TrackerBlock
+        for (int i = 1; i <= 5; i++) {
+            BlockPos above = pos.up(i);
+            if (world.getBlockState(above).getBlock() instanceof TrackerBlock) {
+                cir.setReturnValue(VoxelShapes.empty());
+                return;
+            }
+        }
+    }
+}

src/main/resources/szar.mixins.json

@@ -7,6 +7,7 @@
     "CraftingScreenHandlerMixin",
     "CraftingScreenHandlerMixin2",
     "LivingEntityFallDamageMixin",
+    "NoClipMixin",
     "PlaneBlockInteractionMixin",
     "PlayerEntityMixin",
     "PlayerInteractionMixin",