Subterror Behemoth Stalagmo

FLIP: You can discard 1 "Subterror" monster, and if you do, draw 2 cards. You can only use this effect of "Subterror Behemoth Stalagmo" 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.