msem-instigator

Menace, haste
As long as Arleigh, Spellblade Prodigy is tapped, the first spell you cast during each other player's turn costs {U/R} less to cast. This effect reduces only the amount of colored mana you pay. (For example, if you cast a spell with mana cost {1}{R}, it costs {1} to cast.)

Flying
Once each turn, when a creature an opponent controls dies, you may create a Treasure token.
{3}{B/R}{B/R}: Search target opponent's library for a card and exile it face down. Then that player shuffles. You may look at and play that card for as long as it remains exiled. Activate only once each turn and only as a sorcery.

Whenever you cast a noncreature spell, torment each opponent. (They lose 3 life unless they discard a card or sacrifice a nonland permanent.)
{3}{U/B}{U/B}: Draw a card for each opponent with ten or more cards in their graveyard. You lose that much life.

All creatures get -2/-2 until end of turn. At the beginning of the next end step, if three or more creatures died this turn, create two tapped Treasure tokens.

{1}, Sacrifice a creature: Each opponent loses 1 life and you gain 1 life.

Target creature gets -3/-3 until end of turn. If you control a legendary creature, instead destroy that creature.

Menace, lifelink
Whenever a creature enters under an opponent's control, you may have that player lose 1 life.

At the beginning of your upkeep, you lose 1 life and create a 1/1 white Soldier creature token with melee. (Whenever that creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)

When Scion of Sarrithaz enters, create a 2/2 black Zombie creature token.
{2}{B}, Sacrifice a creature: Draw a card.

Flying
Improve—{1}{B/R}, Sacrifice a creature. ({1}{B/R}, Sacrifice a creature: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Whenever another creature you control dies, each opponent loses 1 life and you gain 1 life. If that creature was sacrificed, instead each opponent loses 2 life and you gain 2 life.

When Ryleth, Vengeful Shadow enters, create two 1/1 green Elf creature tokens.
Whenever you attack, you may pay {1}{B/G}. When you do, return target creature card with mana value less than or equal to the number of attacking creature tokens you control from your graveyard to the battlefield tapped and attacking.

Flying
Rezzal, the Loamfeaster gets +1/+1 for each nonland card exiled with it.
You may play lands exiled with Rezzal.
{1}{B/G}: Exile target card from an opponent's graveyard. Activate only outside of combat.

Menace
Regal Dragoon gets +1/+1 as long as you control a legendary creature.

When Poisoned Shiv enters, destroy target creature or planeswalker.
Equipped creature gets +2/+0 and has deathtouch.
Equip {2}

Deathtouch, lifelink
Improve {1}{W/B} ({1}{W/B}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
{4}: Target creature gains deathtouch and lifelink until end of turn. Activate only during a player's first main phase.

Once during each of your turns, you may cast a legendary creature or planeswalker spell from your graveyard.
Sacrifice Pallid Herald: Exile up to three target cards from graveyards.

Lifelink
At the beginning of your upkeep, Osgaerith Desecrator deals 1 damage to up to one target creature.

Whenever a creature attacks one of your opponents, that player loses 1 life.

{U/B}{U/B}: Return Nherix, the Soulcage from your graveyard to the battlefield tapped.
{6}: Return target creature card with mana value 2 or less from your graveyard to the battlefield tapped.

Creatures your opponents control get -1/-1 until end of turn. You gain 2 life.

When Merciless Blackguard enters, each player sacrifices a creature. For each creature token sacrificed this way, you may create a Treasure token.

Improve {B} ({B}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Whenever a nontoken creature you control dies, if it was embattled, you may pay {B}. If you do, create a 2/2 black Zombie creature token. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Flying, trample
When Lord of Sacrilege enters, each opponent loses 3 life, discards a card, then sacrifices a nonland permanent. If you control three or more Demons and/or Warlocks, instead each opponent loses 6 life, discards two cards, then sacrifices two nonland permanents.

Whenever a creature you control leaves the battlefield, if it had counters on it, you may put one of those counters on Ironpact Marauder.
{1}{B}, Remove two counters from Ironpact Marauder: You draw a card and you lose 1 life.

Destroy all creatures and planeswalkers with mana value X or less.