Geist of the Lonely Vigil

Oracle Text

Defender, flying

Delirium — Geist of the Lonely Vigil can attack as though it didn't have defender as long as there are four or more card types among cards in your graveyard.

Card Rulings

7/13/2016 Once you’ve attacked with Geist of the Lonely Vigil, lowering the number of card types in your graveyard won’t remove it from combat.