When Greta, Sweettooth Scourge enters the battlefield, create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this artifact: You gain 3 life.")
{G}, Sacrifice a Food: Put a +1/+1 counter on target creature. Activate only as a sorcery.
{1}{B}, Sacrifice a Food: You draw a card and you lose 1 life.