Corrupt

Corrupt deals damage to any target equal to the number of Swamps you control. You gain life equal to the damage dealt this way.

Yawgmoth brushed Urza's mind, and Urza's world convulsed.

The List

"Most wise, most thoughtful, most powerful qadir," said the Gixian, "we offer whatever help we may give in your illustrious name."

The Brothers' War

There are things beneath the murk for whom the bog is a stew, a thin broth in need of meat.

Duel Decks Anthology: Garruk vs. Liliana

Corrupt deals damage equal to the number of Swamps you control to target creature or player. You gain life equal to the damage dealt this way.

Duel Decks Anthology: Divine vs. Demonic

The amount of damage dealt to a creature is not bounded by its toughness, and the amount of damage dealt to a player is not bounded by that player's life total. For example, if Corrupt deals 6 damage to a 2/2 creature, you'll gain 6 life.

The life you gain is equal to the damage dealt by Corrupt, not necessarily to the number of Swamps you control (if some or all of the damage is prevented, for example).

Corrupt counts any land you control with the subtype Swamp, not just ones named Swamp.