Subterror Behemoth Stygokraken (Super Rare)

FLIP: You can target Set cards on the field, equal to the number of "Subterror Behemoth" monsters you control, destroy them. You can only use this effect of "Subterror Behemoth Stygokraken" once per turn. When a face-up monster you control is flipped face-down, if you control no face-up monsters: You can Special Summon this card from your hand in Defense Position. Once per turn: You can change this card to face-down Defense Position.