Flowstone Hellion

Haste
{0}: This creature gets +1/-1 until end of turn.

The List

Vintage Masters

Haste
{0}: Flowstone Hellion gets +1/-1 until end of turn.

Stronghold

Flowstone Hellion is unaffected by summoning sickness.
o0: Flowstone Hellion gets +1/-1 until end of turn.

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.