"How can werewolves be considered abominations next to such creatures?"
—Arlinn Kord

Wolf of Devil's Breach

Whenever this creature attacks, you may pay {1}{R} and discard a card. If you do, this creature deals damage to target creature or planeswalker equal to the discarded card's mana value.

Shadows over Innistrad Promos

Shadows over Innistrad

Whenever Wolf of Devil's Breach attacks, you may pay {1}{R} and discard a card. If you do, Wolf of Devil's Breach deals damage to target creature or planeswalker equal to the discarded card's converted mana cost.

If a card with {X} in its mana cost is discarded to Wolf of Devil’s Breach’s ability, X is considered to be 0.

You can’t choose to discard a card without also paying {1}{R}.

You choose the target creature or planeswalker as the triggered ability of Wolf of Devil’s Breach is put onto the stack. You choose which card to discard, if any, as the ability resolves. While players may respond to the triggered ability once you’ve chosen a target, no player may take actions between the time you discard the card and the time damage is dealt.