At the beginning of your upkeep, sacrifice Thelon's Chant unless you pay.
Whenever a player puts a Swamp onto the battlefield, Thelon's Chant deals 3 damage to that player unless the player puts a -1/-1 counter on a creature they control.
10/4/2004 Damages the player putting the land onto the battlefield, even if they are not the controller of the land after it is on the battlefield.
10/4/2004 Only checks the type of the land as it is put onto the battlefield. If the land gets changed after it enters the battlefield (even by a continuous effect), the Chant causes no additional effect.