Lao-Shan Lung, the Siege

This spell costs {1} less to cast for each wall controlled by your opponents.
Trample
When Lao-Shan Lung, the Siege enters the battlefield, each opponent creates two 0/4
colorless wall creature tokens with defender.
Whenever Lao-Shan Lung, the Siege deals
combat damage to a player who doesn't control
a wall, that player loses the game.