Flowstone Hellion

• WWizards of the Coast2004-10-04
  Official Ruling
  It will be put into its owner's graveyard as soon as one of its abilities resolves that puts its toughness at zero (or less than the current amount of damage on it). This is a state-based action, so there is no way to activate its ability any more to increase its power further before it is put into the graveyard.

Rulings via Scryfall