Bog Serpent + Assault Suit

Bog Serpent

Assault Suit

How it works

1. If necessary, at the beginning of the upkeep of an opponent who controls no Swamps, Assault Suit triggers, causing that player to gain control of Bog Serpent and untap it.
2. Bog Serpent triggers, but cannot be sacrificed due to Assault Suit's ability.
3. Step 2 repeats forever, resulting in a mandatory infinite loop that causes the game to end in a draw.