Flying
Acid Breath — When this creature enters, target creature an opponent controls gets -3/-3 until end of turn.

Destroy all creatures. For each nontoken creature destroyed this way, you create a tapped Treasure token.

Exile up to five target creature cards from graveyards. An opponent separates those cards into two piles. Put all cards from the pile of your choice onto the battlefield under your control and the rest into their owners' graveyards.

Flying
At the beginning of your end step, exile the top card of each opponent's library. You may play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.
Whenever a nonland permanent an opponent owns enters under your control, they lose life equal to its mana value.

Each player mills ten cards. For each player, choose a creature or planeswalker card in that player's graveyard. Put those cards onto the battlefield under your control. Then each creature you control becomes a Phyrexian in addition to its other types.

Flying
Whenever this creature or another creature you control dies, each opponent sacrifices a creature of their choice.

When this enchantment enters, if you cast it, destroy all nonenchantment creatures.
Whenever this enchantment or another enchantment you control enters, until end of turn, this enchantment becomes a legendary 6/6 Nightmare God creature with menace and deathtouch. It's still an enchantment.

(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.)
Once during each of your turns, you may cast a spell from your hand by paying life equal to its mana value rather than paying its mana cost.

Enchant player
At the beginning of enchanted player's upkeep, that player sacrifices a creature or planeswalker of their choice. If the player can't, they lose 5 life.

Flying
When this creature enters, if you cast it from your hand and there are five or more other creatures on the battlefield, destroy all other creatures.

Flying
Whenever you gain life, target opponent loses that much life.

Flying, trample
Whenever this creature deals combat damage to a player, that player sacrifices a creature of their choice.

Flying
At the beginning of your end step, sacrifice a non-Demon creature. If you do, create a token that's a copy of this creature.

Delirium — This spell costs less to cast if there are four or more card types among cards in your graveyard.
Flying

As an additional cost to cast this spell, sacrifice a creature, discard a card, or pay 4 life.
When this creature enters, each opponent sacrifices a creature of their choice, discards a card, and loses 4 life.

Flying
, Sacrifice another creature: Regenerate this creature.
, Sacrifice two other creatures: Destroy target creature.

Flying
When this creature enters, you may have target opponent discard a card.

Menace
Whenever this creature attacks a player, exile all cards from that player's hand, then they draw that many cards. You may play lands and cast spells from among the exiled cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.

Flying, lifelink
You may play lands and cast spells from among cards in your graveyard you've surveilled this turn. If you cast a spell this way, you pay life equal to its mana value rather than paying its mana cost.

Whenever this creature deals combat damage to a player, you may return to your hand all creature cards that were put into your graveyard from the battlefield this turn.
, Sacrifice another creature: Target creature gets -2/-2 until end of turn.

Exile all creature cards from target player's graveyard in a face-down pile, shuffle that pile, then manifest those cards.

Whenever this creature becomes blocked by a creature, that creature's controller loses 2 life and you gain 2 life.

Swampcycling
Backup 2
Menace

Whenever a creature you don't control dies, return it to the battlefield under your control with an additional +1/+1 counter on it at the beginning of the next end step. That creature is a black Zombie in addition to its other colors and types.

Roll two d10 and choose one result. Return a creature card from your graveyard to the battlefield with a number of +1/+1 counters on it equal to that result. Then each opponent loses X life and you gain X life, where X is the other result.

Flying
When this creature dies, all creatures get -5/-5 until end of turn.

When this enchantment enters, exile target opponent's graveyard.
You may play lands from among cards exiled with this enchantment.
You may cast spells from among cards exiled with this enchantment. You can't cast more than one spell this way each turn.

Improvise
Flying
At the beginning of your end step, each opponent discards a card.
, Sacrifice an artifact: Target creature gets -2/-2 until end of turn.

Whenever one or more creatures you control become blocked, each blocking creature gets -1/-1 until end of turn.

At the beginning of your upkeep, if you have no cards in hand, each opponent loses 2 life.
At the beginning of each opponent's upkeep, if that player has no cards in hand, they lose 2 life.