The Heironium Arena

This land enters the battlefield tapped.
{t}: Add {r} or {w}.
{x}, {t}, Sacrifice The Heironium Arena: Add X
mana in any combination of colors to your mana
pool. Create a red and white 1/1 Knight creature
token with "{2}, {t}: This creature fights target
creature. When that creature dies this turn,
return The Heironium Arena from your
graveyard to your hand."