Some pre-fix idea's for mobs i just thought of right now. I believe pre-fixed mobs will be more rare then normal mobs, and maybe hopeful they have a chance to drop rarer items.. I know notch said he wanted his mobs to have prefix's, i think these are some obvious choices:
"Giants" - The size of the mobs are increased by 500%, their health are increased by 500% as well. Giants are less aggressive, but if they are provoked they do massive amounts of damage. They have a chance of smashing blocks apart to get towards their target. They are unable to break through solid stone, but are able to smash through dirt and cobble easily.
"Hasted" - The mob's speed is increased by 50%. These mobs have increased attack rate too. When their is a haste creeper, their damage radius is cut in half.
"Burning" - They mobs are enchanted with fire, and when they are provoked they start burning everything in close proximity of them. All of their attacks dealt will cause a lingering fire tick to occur. Since this is enchanted fire, the only way to put the fire out is jump into water. Better have a bucket ready!
"Swarm" - A swarm of mobs is a horrid sight to see. Their will always be at least 5 mobs together when their is a swarm. Luckily because their are so many of them, they are weaken by 50% due having to be closed in so often by their company.
"Chief" - Very rarely a chief is seen controlling a swarm of mobs, but when it does happen, bring some friends with you. a Chief does not only have increased health, damage as well as possibility of wearing armor, but they also can heal mobs with the swarm tag on them as well. It will be a good idea to try to take the chief out first if you should ever encounter this deadly mob.
You say Giants can't smash through solid stone. I think it SHOULD be able to, just not immediately. Like upon first hitting the stone, small cracks develop in it like what you see when you're mining stone and it's almost broken apart, then if it hits it again, it turns to cobble stone, THEN it can break it completely upon the next hit. Don't you think giants should move a little slower too? And maybe not be as persistent as monsters are now? Like monsters now will follow you no matter what, but Giants if they don't see you for a few seconds and it doesn't see you when it breaks a few things, it just goes "Oh well" and walks off.
If they do add these then it should only be on hard or even better on some new difficulties. If you do not agree you are completely brain dead. Because for one there are no reasons not to have it that way and 2 there are many reasons to have it that way.