LivingEntity#setKiller

== AT ==
public net.minecraft.world.entity.LivingEntity lastHurtByPlayerTime

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftLivingEntity.java

@@ -417,6 +417,16 @@ public class CraftLivingEntity extends CraftEntity implements LivingEntity {
         return this.getHandle().lastHurtByPlayer == null ? null : (Player) this.getHandle().lastHurtByPlayer.getBukkitEntity();
     }
 
+    // Paper start
+    @Override
+    public void setKiller(Player killer) {
+        net.minecraft.server.level.ServerPlayer entityPlayer = killer == null ? null : ((CraftPlayer) killer).getHandle();
+        getHandle().lastHurtByPlayer = entityPlayer;
+        getHandle().lastHurtByMob = entityPlayer;
+        getHandle().lastHurtByPlayerTime = entityPlayer == null ? 0 : 100; // 100 value taken from EntityLiving#damageEntity
+    }
+    // Paper end
+
     @Override
     public boolean addPotionEffect(PotionEffect effect) {
         return this.addPotionEffect(effect, false);