Update

src/main/java/systems/brn/tweaks/mixin/DontHurtMePearlMixin.java

@@ -2,6 +2,8 @@ package systems.brn.tweaks.mixin;
 
 import net.minecraft.entity.Entity;
 import net.minecraft.entity.damage.DamageSource;
+import net.minecraft.server.network.ServerPlayerEntity;
+import net.minecraft.server.world.ServerWorld;
 import net.minecraft.world.World;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.injection.At;
@@ -13,11 +15,9 @@ import static systems.brn.tweaks.Tweaks.Enderpearl_Damage;
 public class DontHurtMePearlMixin {
 
     @Redirect(method = "onCollision(Lnet/minecraft/util/hit/HitResult;)V",
-            at = @At(value = "INVOKE",
-                    target = "Lnet/minecraft/entity/Entity;damage(Lnet/minecraft/entity/damage/DamageSource;F)Z"))
-    private boolean redirectDamage(Entity entity, DamageSource source, float amount) {
-        World world = entity.getWorld();
-        entity.damage(source, world.getGameRules().getInt(Enderpearl_Damage));
+            at = @At(value = "INVOKE", target = "Lnet/minecraft/server/network/ServerPlayerEntity;damage(Lnet/minecraft/server/world/ServerWorld;Lnet/minecraft/entity/damage/DamageSource;F)Z"))
+    private boolean redirectDamage(ServerPlayerEntity entity, ServerWorld world, DamageSource source, float amount) {
+        entity.damage(world, source, world.getGameRules().getInt(Enderpearl_Damage));
         return false;
     }
 }

src/main/java/systems/brn/tweaks/mixin/JustTeleportAlreadyMixin.java

@@ -1,5 +1,6 @@
 package systems.brn.tweaks.mixin;
 
+import net.minecraft.server.world.ServerWorld;
 import net.minecraft.world.World;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.Shadow;
@@ -12,22 +13,28 @@ import static systems.brn.tweaks.Tweaks.Entity_Portal_Cooldown;
 
 @Mixin(net.minecraft.entity.Entity.class)
 public class JustTeleportAlreadyMixin {
-    @Shadow private World world;
+    @Shadow
+    private World world;
 
     @Inject(method = "getDefaultPortalCooldown",
             at = @At(value = "RETURN"),
             cancellable = true)
     private void getDefaultPortalCooldown(CallbackInfoReturnable<Integer> cir) {
-        cir.setReturnValue(world.getGameRules().getInt(Entity_Portal_Cooldown));
+        if (world instanceof ServerWorld sWorld) {
+            cir.setReturnValue(sWorld.getGameRules().getInt(Entity_Portal_Cooldown));
+        }
     }
 
     @Shadow
     private int portalCooldown;
+
     @Inject(method = "tickPortalCooldown", at = @At(value = "RETURN"))
     private void tickPortalCooldown(CallbackInfo ci) {
-        int maxCooldown = world.getGameRules().getInt(Entity_Portal_Cooldown);
-        if (portalCooldown > maxCooldown) {
-            portalCooldown = maxCooldown;
+        if (world instanceof ServerWorld sWorld) {
+            int maxCooldown = sWorld.getGameRules().getInt(Entity_Portal_Cooldown);
+            if (portalCooldown > maxCooldown) {
+                portalCooldown = maxCooldown;
+            }
         }
     }
 }