Omnath, Locus of the Void is a rare Legendary Creature — Elemental card from Reality Fracture Commander (FRC), collector number 3. Current market price: $3.13, TCGplayer market prices via Scryfall.
Omnath gets +1/+1 for each unspent mana you have. If you would lose unspent mana, that mana becomes colorless instead. Landfall — Whenever a land you control enters, add {C}{C}.