Change the appearance of a falling anvil to a flaming block.

FlamingAnvil.java

package com.comphenix.example;

import java.util.HashSet;
import java.util.Set;

import org.bukkit.ChatColor;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.FallingBlock;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDeathEvent;
import org.bukkit.plugin.java.JavaPlugin;

import com.comphenix.protocol.Packets;
import com.comphenix.protocol.ProtocolLibrary;
import com.comphenix.protocol.events.ConnectionSide;
import com.comphenix.protocol.events.PacketAdapter;
import com.comphenix.protocol.events.PacketEvent;

public class FlamingAnvil extends JavaPlugin implements Listener {
    private Set<Integer> flamingBlocks = new HashSet<Integer>();
    private boolean spawningFlamingBlocks;
    
    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(this, this);
        
        ProtocolLibrary.getProtocolManager().addPacketListener(new PacketAdapter(this, ConnectionSide.SERVER_SIDE, Packets.Server.VEHICLE_SPAWN) {
        @Override
            public void onPacketSending(PacketEvent event) {
                int entityID = event.getPacket().getIntegers().read(0);
                
                // See if we just spawned it
                if (spawningFlamingBlocks) {
                    flamingBlocks.add(entityID);
                }
                if (flamingBlocks.contains(entityID)) {
                    // Set the material for the client. Look at PacketWrapper's Packet17SpawnObjectVehicle for more information.
                    event.getPacket().getIntegers().write(10, Material.FIRE.getId());
                }
            }   
        });
    }
    
    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (sender instanceof Player) {
            spawnFireBlock((Player) sender);
        } else {
            sender.sendMessage(ChatColor.RED + "This command is only supported for players.");
        }
        return true;
    }
    
    @EventHandler
    public void onEntityDeathEvent(EntityDeathEvent e) {
        // Clean up
        flamingBlocks.remove(e.getEntity().getEntityId());
    }
    
    private void spawnFireBlock(Player player) {
        // Indicate that we're currently spawning fire blocks
        spawningFlamingBlocks = true;
        
        Location above = player.getLocation().add(0, 10, 0);
        FallingBlock block = player.getWorld().spawnFallingBlock(above, Material.ANVIL, (byte) 0);
        
        // We're done - add the entity ID just in case
        spawningFlamingBlocks = false;
        flamingBlocks.add(block.getEntityId()); 
    }
}