Ravenous Trap

If an opponent had three or more cards put into their graveyard from anywhere this turn, you may pay {0} rather than pay this spell's mana cost.
Exile target player's graveyard.

Double Masters

If an opponent had three or more cards put into their graveyard from anywhere this turn, you may pay {0} rather than pay this spell's mana cost.
Exile all cards from target player's graveyard.

The List

Zendikar

If an opponent had three or more cards put into his or her graveyard from anywhere this turn, you may pay {0} rather than pay Ravenous Trap's mana cost.
Exile all cards from target player's graveyard.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as Ravenous Trap's alternative cost), add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.