Nahûr, the Powder-Singer

: Nahûr the Powder-Singer's "X" cost can be paid with any mana, even mana with specific conditions to be spent.
-X: Deal X damage to target Creature, Battle or Planeswalker. Creatures, Battles and Planeswalkers cannot be destroyed by this ability.
-3: Deal 4 damage to the next enemy unit that gets tapped or that activates it's ability.