In Minecraft they should have different personalitys for the same mob. For Example I wouldn't mind diffrent types of creepers like a water creeper, cookie creeper (which explodes with cookoies :rolleyes:),Earth Creeper, or even a friendly creeper. I think if they introduce this to Minecraft there will be much more variety and alot more interaction in the game
Prefixes are possible, but highly unlikely. It's pointless really. All they're going to be are mobs that look like something else. Doesn't matter if they have more health or whatever, they still are only really mobs that look different.
Notch confirmed during the Brocraft.net stream that he will be adding prefix mobs. This means that there will be mobs such as 'Burning Spider' 'Giant Zombie' 'Cobble Creeper', etc. It is not known if these are still planned to be in a future update. However, the dreaded Cave Spider and technically the Charged Creeper are prefix mobs.
Not a bad idea, but I'd go along with how they'll interact with the environment. Like a Fire Creeper starts a fire when it explodes. Not so bad when on stone... but on wood or in trees, bad. Water Creeper could create a water source when it explodes and start flooding something. Earth Creeper could add Dirt instead of blowing it up. Perhaps your Friendly Creeper would be able to de-aggro the other Creepers.
Edit: Here, on the Wiki:
http://www.minecraftwiki.net/wiki/Mobs#Potential_Future_Mobs
[quote=Badgerz]You have to keep in mind that people are stupid.
[quote=Catelite]Just because you don't understand how something works, doesn't make it broken or pointless. >_<
I would do the same.