Entities

Entities Skill — Paper

Purpose

Reference this skill when spawning, customising, or removing entities in Paper 1.21. Covers mob spawning, attribute modification, equipment, Display entities, and the EntitySpawnEvent.

When to Use This Skill

• Spawning a custom mob with modified health, speed, or damage
• Creating a floating text label using TextDisplay
• Attaching equipment (armour, held items) to a mob
• Preventing specific entity types from spawning via events

API Quick Reference

Code Pattern

package com.yourorg.myplugin.entities;

import net.kyori.adventure.text.Component;
import net.kyori.adventure.text.format.NamedTextColor;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.attribute.Attribute;
import org.bukkit.attribute.AttributeInstance;
import org.bukkit.attribute.AttributeModifier;
import org.bukkit.entity.EntityType;
import org.bukkit.entity.TextDisplay;
import org.bukkit.entity.Zombie;
import org.bukkit.inventory.EquipmentSlotGroup;
import org.bukkit.inventory.ItemStack;
import org.bukkit.plugin.java.JavaPlugin;

import java.util.UUID;

public class EntitySpawner {

    private final JavaPlugin plugin;

    public EntitySpawner(JavaPlugin plugin) {
        this.plugin = plugin;
    }

    // Spawn a custom boss zombie with buffed stats and equipment
    public Zombie spawnBossZombie(Location location) {
        return location.getWorld().spawn(location, Zombie.class, zombie -> {
            // Pre-spawn configurator — fires before EntitySpawnEvent

            // Custom name tag
            zombie.customName(Component.text("☠ Dungeon Boss").color(NamedTextColor.RED));
            zombie.setCustomNameVisible(true);

            // Double max health
            AttributeInstance maxHealth = zombie.getAttribute(Attribute.GENERIC_MAX_HEALTH);
            if (maxHealth != null) maxHealth.setBaseValue(100.0);
            zombie.setHealth(100.0);

            // Speed boost via modifier
            AttributeInstance speed = zombie.getAttribute(Attribute.GENERIC_MOVEMENT_SPEED);
            if (speed != null) {
                speed.addModifier(new AttributeModifier(
                    new org.bukkit.NamespacedKey(plugin, "boss_speed"),
                    0.1,
                    AttributeModifier.Operation.ADD_NUMBER,
                    EquipmentSlotGroup.ANY
                ));
            }

            // Equipment
            var equipment = zombie.getEquipment();
            if (equipment != null) {
                equipment.setHelmet(new ItemStack(Material.DIAMOND_HELMET));
                equipment.setItemInMainHand(new ItemStack(Material.DIAMOND_SWORD));
                // Prevent drops
                equipment.setHelmetDropChance(0.0f);
                equipment.setItemInMainHandDropChance(0.0f);
            }

            // Don't burn in sunlight
            zombie.setCanPickupItems(false);
        });
    }

    // Spawn a floating text label using TextDisplay (Paper 1.19.4+)
    public TextDisplay spawnFloatingText(Location location, String text) {
        return location.getWorld().spawn(location, TextDisplay.class, display -> {
            display.text(Component.text(text)
                .color(NamedTextColor.YELLOW));
            display.setBillboard(org.bukkit.entity.Display.Billboard.CENTER);   // always faces player
            display.setBackgroundColor(org.bukkit.Color.fromARGB(100, 0, 0, 0)); // semi-transparent bg
        });
    }
}

Common Pitfalls

• Using EntityType enum with spawnEntity instead of typed spawn: spawnEntity(loc, EntityType.ZOMBIE) returns Entity which requires an unsafe cast. Use spawn(loc, Zombie.class) for type-safe access.

• Setting health before setting max health: Calling setHealth(100) when max health is still 20 caps it at 20. Always set the GENERIC_MAX_HEALTH attribute base value first.

• Not calling setCustomNameVisible(true): Setting a custom name without this flag hides it unless the player mouses over the mob.

• Entities despawning due to mob caps: Spawned mobs count toward the world mob cap and may despawn if no player is nearby. Call entity.setPersistent(true) to prevent despawning.

• AttributeModifier UUID collision: Using UUID.randomUUID() each time creates a new modifier every plugin reload, which stacks. Use a stable NamespacedKey-based constructor (Paper 1.21 API) instead.

Version Notes

• 1.21: AttributeModifier constructor with NamespacedKey is preferred over the UUID-based one (deprecated). EquipmentSlotGroup.ANY replaces the old EquipmentSlot parameter.
• 1.21: TextDisplay, ItemDisplay, BlockDisplay (Display entities) are stable and available.
• 1.21.1: No breaking changes to entity API.

Related Skills

• entity-management.md — Full attribute reference, equipment slots, Display entity options
• ../events/world-events.md — EntityDamageEvent, EntitySpawnEvent
• ../storage/pdc.md — Tagging entities with PDC for identity