Each creature card in your graveyard has scavenge. The scavenge cost is equal to its mana cost. (Exile a creature card from your graveyard and pay its mana cost: Put a number of +1/+1 counters equal to that card's power on target creature. Scavenge only as a sorcery.)
Sacrifice another creature: Regenerate Varolz, the Scar-Striped.
4/15/2013 Exiling the creature card with scavenge is part of the cost of activating the scavenge ability. Once the ability is activated and the cost is paid, it’s too late to stop the ability from being activated by trying to remove the creature card from the graveyard.
4/15/2013 While Varolz, the Scar-Striped is on the battlefield, the scavenge cost of a creature card in your graveyard is equal to its mana cost, including any colored mana requirements.
4/15/2013 Abilities that reduce the cost to cast a creature spell or alternative costs you can pay rather than a card’s mana cost don’t apply to activating a card’s scavenge ability.
4/15/2013 The number of counters that a card’s scavenge ability puts on a creature is based on the card’s power as it last existed in the graveyard.
4/15/2013 If the creature card you scavenge has in its mana cost, X is 0.
4/15/2013 If a creature card has multiple instances of scavenge, you can activate either ability (but not both, as the card will be exiled when you activate one of them). Varolz’s ability doesn’t affect the scavenge cost of a creature’s other scavenge ability.