You cannot Special Summon from the Extra Deck, except "Number" Xyz Monsters. You can only use each of the following effects of "Gorgonic Umbral Horror" once per turn. If you control no monsters, or all monsters you control are "Umbral Horror" monsters: You can Special Summon this card from your hand, and if you do, add 1 non-Rock "Umbral Horror" monster from your Deck to your hand. Can be treated as 2 materials for the Xyz Summon of a "Number" Xyz Monster that requires 3 or more materials.