Flying
Whenever Xyru Specter deals damage to an opponent, that player discards a card unless they challenge you. If challenged, and you show them two black cards in your hand, they must discard two cards.
If you’re challenged, you may reveal any number of cards from your hand. The effect that allowed a player to challenge you will specify what you must reveal to win the challenge.
“Summon” isn’t a card type. Xyru Specter is a creature.