I'm currently working out the logistics for the mob customization for my mod (ApocalypseCraft), and I'm running through different possible methodologies for adapting mob behavior. I've seen systems where mobs with alternate characteristics are tacked by a code module which with the help of some listeners dictates what happens next in the mob's behavior chain. I'm curious though about what the most "proper" way to go about altering a mob's behavior is, however. Hypothetically, if I wanted to write a non-hostile flaming (albeit fire-proof) creeper that follows the player and doesn't explode, then what would be the best approach to do this? I'm in no way expecting anyone to write the code for me since I'm more than capable of doing so myself, but I'm at a loss for deciphering the most appropriate (non-fragile) way of customizing mob behavior in Bukkit.