Lorwyn

Wanderwine Prophets

Champion a Merfolk (When this comes into play, sacrifice it unless you remove another Merfolk you control from the game. When this leaves play, that card returns to play.)
Whenever Wanderwine Prophets deals combat damage to a player, you may sacrifice a Merfolk. If you do, take an extra turn after this one.

Champion a Merfolk (When this enters, sacrifice it unless you exile another Merfolk you control. When this leaves the battlefield, that card returns to the battlefield.)
Whenever Wanderwine Prophets deals combat damage to a player, you may sacrifice a Merfolk. If you do, take an extra turn after this one.