Serperior (13/149) [Black & White: Boundaries Crossed] Fox Monk Set: Mirrodin Type: Artifact Rarity:

Set: Mirrodin Type: Artifact Rarity: Rare Cost: {5} Whenever an opponent draws a card

Set: Arena League 2001 Type: Instant Rarity: Rare Cost: {1}{B} Target player sacrifices a creature

Set: Legends Type: Creature — Human Rarity: Rare Cost: {2}{G}{G} {2}{G}{G}: Create a 1/1 green Wolf creature token named Wolves of the Hunt

but it explains much

If the creature that spell becomes as it resolves has not been turned face up and would assign or deal damage

Serperior (13/149) [Black & White: Boundaries Crossed] Fox Monk Set: Mirrodin Type: Artifact Rarity:Set: Black & White: Boundaries Crossed Type: Grass Rarity: Holo Rare Retreat cost: Colorless