Illhoof is kind of a silly name. They couldn't at least give him a menacing title?

Our Karazhan guide has been updated once more, now displaying the strategy to defeat the demon, Illhoof, inhabiting Medivh's Library. So stop wondering how to deal with that many imps at once, and check out our newly updated guide!

An optional boss in the repository of Karazhan, this demon is a fun challenge and extra loot for your raid should you have time.
You may access his area by opening a bookcase in the Library wing and heading down the ramp - there's very few monsters in the way, namely imps and demons, but nothing too harsh for your raid.

Give it a look at Ten Ton Hammer's WoW site.