+Abyss (14)
When Abyssal Gatekeeper dies, each player sacrifices a creature of their choice.
When Abyssal Gorestalker enters, each player sacrifices two creatures of their choice.
: Exile target creature card from a graveyard that was put there this turn. Create a token that's a copy of it, except it's a Nightmare in addition to its other types. Then exile all other Nightmare tokens you control.
Flying
When Abyssal Horror enters, target player discards two cards.
, : Tap target creature. Abyssal Hunter deals damage equal to Abyssal Hunter's power to that creature.
Whenever Abyssal Nightstalker attacks and isn't blocked, defending player discards a card.
Whenever an opponent discards a card, Abyssal Nocturnus gets +2/+2 and gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)
Flying, trample
You can't win the game and your opponents can't lose the game.
Whenever Abyssal Specter deals damage to a player, that player discards a card.
At the beginning of each player's upkeep, destroy target nonartifact creature that player controls of their choice. It can't be regenerated.
Target player draws cards equal to half the number of cards in their library and loses half their life. Round up each time.
Morbid — At the beginning of each end step, if a creature died this turn, destroy target non-Demon creature.
At the beginning of your upkeep, destroy all nonland permanents with the first name alphabetically among nonland permanents.
Gatherer works better in the Companion app!
: Exile target creature card from a graveyard that was put there this turn. Create a token that's a copy of it, except it's a Nightmare in addition to its other types. Then exile all other Nightmare tokens you control.