Spiteful Visions

At the beginning of each player's draw step, that player draws an additional card.
Whenever a player draws a card, Spiteful Visions deals 1 damage to that player.

Spellshock

Whenever a player casts a spell, Spellshock deals 2 damage to that player.

Dragon's Rage Channeler

Whenever you cast a noncreature spell, surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)
Delirium — As long as there are four or more card types among cards in your graveyard, Dragon's Rage Channeler gets +2/+2, has flying, and attacks each combat if able.

Doomwake Giant

Constellation — Whenever Doomwake Giant or another enchantment enters the battlefield under your control, creatures your opponents control get -1/-1 until end of turn.

Forgeborn Oreads

Constellation — Whenever Forgeborn Oreads or another enchantment enters the battlefield under your control, Forgeborn Oreads deals 1 damage to any target.

Archetype of Aggression

Creatures you control have trample.
Creatures your opponents control lose trample and can't have or gain trample.

Mogis, God of Slaughter

Indestructible
As long as your devotion to black and red is less than seven, Mogis isn't a creature.
At the beginning of each opponent's upkeep, Mogis deals 2 damage to that player unless they sacrifice a creature.

Polluted Bonds

Whenever a land enters the battlefield under an opponent's control, that player loses 2 life and you gain 2 life.

Bloodchief Ascension

At the beginning of each end step, if an opponent lost 2 or more life this turn, you may put a quest counter on Bloodchief Ascension. (Damage causes loss of life.)
Whenever a card is put into an opponent's graveyard from anywhere, if Bloodchief Ascension has three or more quest counters on it, you may have that player lose 2 life. If you do, you gain 2 life.

Descent into Avernus

At the beginning of your upkeep, put two descent counters on Descent into Avernus. Then each player creates X Treasure tokens and Descent into Avernus deals X damage to each player, where X is the number of descent counters on Descent into Avernus.

Koskun Falls

At the beginning of your upkeep, sacrifice Koskun Falls unless you tap an untapped creature you control.
Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Court of Ambition

When Court of Ambition enters the battlefield, you become the monarch.
At the beginning of your upkeep, each opponent loses 3 life unless they discard a card. If you're the monarch, instead each opponent loses 6 life unless they discard two cards.

Agent of Erebos

Constellation — Whenever Agent of Erebos or another enchantment enters the battlefield under your control, exile target player's graveyard.

Firebrand Archer

Whenever you cast a noncreature spell, Firebrand Archer deals 1 damage to each opponent.

Manabarbs

Whenever a player taps a land for mana, Manabarbs deals 1 damage to that player.

Price of Glory

Whenever a player taps a land for mana, if it's not that player's turn, destroy that land.

Cacophony Unleashed

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

Thoughtrender Lamia

Constellation — Whenever Thoughtrender Lamia or another enchantment enters the battlefield under your control, each opponent discards a card.

Fate Unraveler

Whenever an opponent draws a card, Fate Unraveler deals 1 damage to that player.

Underworld Dreams

Whenever an opponent draws a card, Underworld Dreams deals 1 damage to that player.

Grim Guardian

Constellation — Whenever Grim Guardian or another enchantment enters the battlefield under your control, each opponent loses 1 life.

Oubliette

When Oubliette enters the battlefield, target creature phases out until Oubliette leaves the battlefield. Tap that creature as it phases in this way. (Auras and Equipment phase out with it. While permanents are phased out, they're treated as though they don't exist.)

Bothersome Quasit

Menace
Goaded creatures your opponents control can't block.
Whenever you cast a noncreature spell, goad target creature an opponent controls. (Until your next turn, that creature attacks each combat if able and attacks a player other than you if able.)

Eidolon of the Great Revel

Whenever a player casts a spell with mana value 3 or less, Eidolon of the Great Revel deals 2 damage to that player.

Havoc Festival

Players can't gain life.
At the beginning of each player's upkeep, that player loses half their life, rounded up.

Erebos, God of the Dead

Indestructible
As long as your devotion to black is less than five, Erebos isn't a creature. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)
Your opponents can't gain life.
{1}{B}, Pay 2 life: Draw a card.

Sulfuric Vortex

At the beginning of each player's upkeep, Sulfuric Vortex deals 2 damage to that player.
If a player would gain life, that player gains no life instead.

Maddening Hex

Enchant player
Whenever enchanted player casts a noncreature spell, roll a d6. Maddening Hex deals damage to that player equal to the result. Then attach Maddening Hex to another one of your opponents chosen at random.