Rotcore, Corrupted Lifewalker

Whenever another nontoken creature dies, choose one:
-Put X +1/+1 counters on Rotcore, where X is equal to the creature's converted mana cost.
OR
-Put an 0/1 black and green Plant Zombie creature token onto the battlefield. It has "Sacrifice this creature: Add {b} or {g} to your mana pool."