(you may cast either half. that door unlocks on the battlefield. as a sorcery, you may pay the mana cost of a locked door to unlock it.)
polluted cistern
whenever one or more cards are put into your graveyard from your library, each opponent loses 1 life for each card type among those cards.
dim oubliette
when you unlock this door, mill three cards, then return a creature card from your graveyard to the battlefield.