A Brain Card is a card which requires intelligence, memory, or knowledge for a certain effect.
Word Cards[]
Word Cards force a person to come up with a certain word, length of word, or amount of words from preselected letters. This type of card is notable for imitating Scrabble or Boggle often. The challenge can be timed or untimed, so long as a person must find a word from letters. Cheating on these cards with fake words is frequent, and is unofficially named Kwyjibo.
Math Cards[]
A Math Card is any card which requires complex calculations in any variable other than one's Score. Math Cards frequently become Useless Cards since they typically become long, incomprehensible equations.
Esoteric Knowledge Cards[]
Sometimes, these cards can require you to know trivia. Of course, these will often get suckboxed, half because certain players are a lot more likely to know what the actual answer is, and half because in the next game, everyone will already have heard the answer. This isn't like Trivial Pursuit, unless you have a deck full of these, they're often Useless Cards. (If you have a deck full of these, then you might as well play Trivial Pursuit.)