Liberator, Urza's Battlethopter [The Brothers' War] H30 Exile an Elf card from

Exile an Elf card from your graveyard: Scarred Vinebreeder gets +3/+3 until end of turn

and certainly not in any of the sliver labs

When you find enough clues to learn what's really going on

Carnifex Demon enters the battlefield with two -1/-1 counters on it

Liberator, Urza's Battlethopter [The Brothers' War] H30 Exile an Elf card fromSet: The Brothers' War Type: Legendary Artifact Creature Thopter Rarity: Rare Cost: {3} Flash Flying You may cast colorless spells and artifact spells as though they had flash. Whenever you cast a spell, if the amount of mana spent to cast that spell is greater than Liberator, Urza's Battlethopter's power, put a +1 +1 counter on Liberator.