Q u o t e: Well right, this is why it won't really be in game. There are things they'll likely want to keep hidden from the normal user (such as damage calculations, etc) but will be found on wiki's and fansites without a doubt. Plus, i'd much rather CTRL+F or search a fansite than have to flip through hundreds of pages of statistics in-game anyway.
Well including an in-game bestiary wouldn't eliminate those fact sheets on fan sites and I don't think he wanted numbers or anything besides health to be displayed. And by health I was imagining the health bar that is standard in D2, except you'd have to earn it for killing them x number of times.
It makes sense in my mind that you'd have to kill something x number of times to understand/know how close to death it is based on the damage you've inflicted (which would be displayed in the form of a health bar). In the same way, it makes sense that after a while you'd learn what that type of damage that monster is weak/strong against and this would be displayed in much the same way it was in D2, e.g. "Cold Immune, Fire Immune, etc" located under the health bar.
The health bar and resistances could be displayed by default if it's a unqiue monster so people know what they're dealing with, but to give those 100%ers something to do, the special skills could be switched for the health bar/resistances for unlocks after x kills. E.g. teleportation is displayed under the health bar for Baal after x kills.