Theater of Horrors

Mana cost: {1}{B}{R}
Type: Enchantment
Set: Forgotten Realms Commander #194 (rare)
Price: $0.39 USD

At the beginning of your upkeep, exile the top card of your library.
During your turn, if an opponent lost life this turn, you may play lands and cast spells from among cards exiled with this enchantment.
{3}{R}: This enchantment deals 1 damage to target opponent or planeswalker.

Theater of Horrors has 5 printings, first in Ravnica Allegiance (2019). EDHREC ranks it #4,829 among Commander cards. It appears most in Valgavoth, Harrower of Souls decks (6,315 on EDHREC). 3 public decks on TCG run it. It has 4 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Public decks that run Theater of Horrors

Chaos Incarnate - Starter Commander Decks, led by Kardur, Doomscourge
Endless Punishment - Duskmourn: House of Horror Commander, led by Valgavoth, Harrower of Souls
Planar Portal - Forgotten Realms Commander, led by Prosper, Tome-Bound

Commanders that run Theater of Horrors most

Deck counts from EDHREC.

Valgavoth, Harrower of Souls: 6,315 decks
Prosper, Tome-Bound: 5,305 decks
Gev, Scaled Scorch: 3,177 decks
Rakdos, Lord of Riots: 2,726 decks
Kardur, Doomscourge: 1,507 decks
The Lord of Pain: 1,323 decks
Fire Lord Zuko: 852 decks
Judith, Carnage Connoisseur: 662 decks

Often played with Theater of Horrors

Cards that show up in the same decks on EDHREC.

Rulings

2019-01-25: Theater of Horrors doesn't change when you can play the exiled cards during your turn. For example, if you exile a sorcery card, you can cast it only during your main phase when the stack is empty. If you exile a land card, you can play it only during your main phase and only if you have an available land play remaining.
2019-01-25: Casting an exiled card causes it to leave exile. You can't cast it multiple times.
2019-01-25: Damage dealt to a player causes that player to lose that much life.
2019-01-25: In a multiplayer game, if an opponent loses life during your turn and then leaves the game, you can play cards exiled with Theater of Horrors.