Katakros, Chosen of Nagash

Double Strike, Prowess
Other Skeletons, Shades, Spirits and Zombies
you control have Prowess.
Whenever another creature enters the battlefield,
if it entered from your graveyard or you cast it
from your graveyard, mill four cards. You may
return a noncreature card from among the cards
milled this way into your hand. This ability
triggers only once each turn.