If the exiled creature has {X} in its mana cost (such as Protean Hydra), X is considered to be zero.
Nemesis Trap
If you cast Nemesis Trap for {B}{B}, you may still target any attacking creature, not just the white attacking creature.
An "attacking creature" is one that has been declared as an attacker this combat, or one that was put onto the battlefield attacking this combat. Unless that creature leaves combat, it continues to be an attacking creature through the end of combat step, even if the player it was attacking has left the game, or the planeswalker it was attacking has left combat.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Ryan Pancoast
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
