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.
Attack power increased by 70.
Rogue, Hunter, Warrior, Druid, Shaman
Down the rabbit hole... Dementia: Damage and healing from spells and effects is increased. (5% for 5 secs) Dementia: Damage and healing from spells and effects is reduced. (5% for 5 secs)
Druid, Shaman, Priest, Warlock, Mage
Agility increased by 35.
Warrior, Rogue, Hunter, Druid
Spell, melee, and ranged haste rating increased by 35.
Spell, melee, and ranged critical strike rating increased by 35.
All classes except Hunter, Paladin
Strength increased by 35.
Paladin, Rogue, Druid, Warrior
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).