RD/KP05-JP063 Maraimei (Magical Dark Lightning) / Maraimei, the Magical Fire
Normal Trap
{Requirement} If you control a face-up “Summoned Skull” or a face-up Normal Monster (Level 7 or higher Fiend), when your opponent Normal or Special Summons a monster(s) (Level 6 or higher) face-up.
{Effect} You take damage equal to [the number of monsters in your opponent’s Graveyard] x 100. Then, shuffle all monsters in your opponent’s Graveyard into the Deck.

Source