Undocumented Changes

[Lissa]

There are invisible mobs in the game now (Dire Maul West). If I had to guess, I'd bet they found that warlocks with detect greater invisibility could too-easily hunt higher level mages.

There have been invisible mobs in the game since Beta. The shades in Stratholme, invisible. Ghosts in DMWest, invisible. They've always been this way. Most people don't realize it, but by having a warlock along or having someone with items that can detect invisible you can take out those pesky shades in Strat before they even pop out and make their yell.