Rat Race

At the beginning of each player's upkeep, that player creates X tapped 1/1 black Rat creatures, where X is the number of Rats he or
she controls plus one. (For example, if a player controls two Rats, he or she creates three more Rats.)
At the beginning of each player's end step, if that player controls thirty or more Rats, he or she loses the game.
Prosperity is its own disease.