Historical Rules · 29 September 2017
Rule 702.1a
Official source text from the 29 September 2017 Rules release
If an effect refers to a “[keyword ability] cost,” it refers only to the variable costs for that keyword. Example: Varolz, the Scar-Striped has the following ability: “Each creature card in your graveyard has scavenge. The scavenge cost is equal to its mana cost.” A creature card’s scavenge cost is an amount of mana equal to its mana cost, and the activation cost of the scavenge ability is that amount of mana plus “Exile this card from your graveyard.”