Shadow Delver (TAEV-EN027) - Tactical Evolution Unlimited

"This card is treated as a Normal Monster while face-up on the field or in the Graveyard. While this card is face-up on the field, when performing the Second Summon of this card, this card becomes an Effect Monster and gains the following effect:
Select 1 face-up Level 4 or lower DARK monster on your side of the field. During this turn the selected monster can attack your opponent's Life Points directly. You may only use this effect once per turn."