MAGIC: THE GATHERING
Search your library for a card and put that card into your hand. Then shuffle your library.
Spell mastery - If there are two or more instant and/or sorcery cards in your graveyard, add to your mana pool.
This powerful spell is basically a Demonic Tutor stapled to a Dark Ritual. As you can imagine, that's a pretty potent combination. Dark Petition quickly found its way into Vintage and Legacy combo decks and is also a great fit in most black Commander decks.