Paradusha, the Paradox

Double Strike, Flying
Whenever Paradusha attacks, you may pay {x}. If you do, Paradusha gets +X/+0 and loses Double Strike until end of turn
Whenever mana leaves your mana pool, if it wasn't spent, you lose that much life. At the beginning of your upkeep, you gain 1 life for each tapped land you control.