Darkmoon Card: Madness

Source
The Lunacy Deck can be turned in at Darkmoon Faire to get the Darkmoon Card: Madness. In addition to 51 stamina, this trinket has an effect that whenever you land a killing blow on a target, you randomly get one of the following buffs (in which your class is listed):

Each buff lasts for 60 seconds.

Trivia
When one of the powers procs, there is a chance your character will say "This is Madness!" This is most likely a reference to the movie 300, and the infamous Sparta quote. The exclamation only appears to the character using the trinket, not to nearby players or even group members (at least as of patch 4.0.1).