Noxious Dragon

Oracle Text

Flying

When Noxious Dragon dies, you may destroy target creature with converted mana cost 3 or less.

Card Rulings

11/24/2014 A face-down creature has a converted mana cost of 0. However, its converted mana cost changes when it’s turned face up. Thus, if a creature is turned face up in response to being targeted by Noxious Dragon’s ability, it may become an illegal target.