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.

If the creature card you scavenge has in its mana cost, X is 0.

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.

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.

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.

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.