Brigid, Clachan’s Heart [Lorwyn Eclipsed Promos] – Trendy Electric Mobility Gear for Modern Riders

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 this creature deals combat damage to a player, you may sacrifice a Merfolk. If you do, take an extra turn after this one.