Skullmane Baku is a common Creature — Spirit card from Betrayers of Kamigawa (BOK), collector number 83. Current market price: $0.07 (foil $0.60), TCGplayer market prices via Scryfall.
Whenever you cast a Spirit or Arcane spell, you may put a ki counter on this creature. {1}, {T}, Remove X ki counters from this creature: Target creature gets -X/-X until end of turn.