Digsite Conservator

Sacrifice this creature: Exile up to four target cards from a single graveyard. Activate only as a sorcery.
When this creature dies, you may pay . If you do, discover 4. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)