msem-instigator

As an additional cost to cast this spell, sacrifice a creature.
Torment target player three times. (They lose 3 life unless they discard a card or sacrifice a nonland permanent.)

Creatures you control get +1/+1 until end of turn. You gain 3 life.
Memento {4}{W}{W} (You may cast this from your graveyard for {4}{W}{W}. If you do, put it onto the battlefield transformed after it resolves. Exile it if it would leave the battlefield or not resolve.)

{1}, {T}, Sacrifice Aureate Panorama: Search your library for a land card that could produce each color of mana, put it onto the battlefield, then shuffle.

Menace
Whenever Auros, Flame-Cursed attacks, it deals 3 damage to each opponent.

Search your library for a permanent card with mana value 3 or less and put it onto the battlefield, then shuffle.
Motley — Then if there are five or more names among nonland permanents you control, you gain 7 life.

{T}: Add {C}.
Sacrifice a nonland permanent: Ayala's Effigy becomes a 2/2 Construct artifact creature until end of turn.

Ayala, Shrouded Shepherd can't attack or block unless your life total is greater than or equal to your starting life total.
Lifelink, indestructible
Whenever a creature attacks you or a planeswalker you control, you may pay {2}. If you do, create a 1/1 white Spirit creature token with lifelink blocking that creature.

Counter target planeswalker spell.
Draw a card.

Haste
Whenever Banished Companion attacks, it deals 2 damage to you.

Sacrifice a creature: Put a +1/+1 counter on Bloodlash Caravan. Then if it's the only creature you control, it gains indestructible until end of turn.

Whenever a creature you control becomes the target of a spell or ability, counter it unless its controller pays {1}. Whenever they do, put a +1/+1 counter on Brushcover Elf. (This includes your spells and abilities.)

Haste
Caulte Axeslinger gets +2/+2 as long as any opponent lost exactly 3 life this turn.

Other nonland permanents enter tapped.
Your opponents can't activate abilities of tapped permanents.

Double strike
Motley — As long as there are five or more names among nonland permanents you control, Champion of Blades has vigilance, trample, and haste.

Equipped creature has haste.
Sacrifice Cinderblade: Equipped creature gains +2/+2 until end of turn.
Equip {1}

Discard a card: Concealed Slasher gets +1/+1 until end of turn and can't be blocked this turn.

Flying
When Cormoran, Raven Monarch enters, you may put target creature card with mana value 3 or less from a graveyard onto the battlefield under your control.

Whenever an opponent casts a spell, that player gets a poison counter unless they pay {1}.
As long as an opponent has five or more poison counters, Corrupted Soothsayer gets +2/+1 and has flying.

Whenever one or more cards leave your graveyard, each opponent loses 1 life and you gain that much life.

This spell costs {X} less to cast, where X is 20 minus your life total.
First strike, menace, trample

Haste
{R}{R}{R}, Discard your hand, Sacrifice Crimson Knight: Draw three cards.

Dawnlit Battlefield enters tapped.
{T}: Add {R} or {W}.
{2}{R}{W}: Until end of turn, Dawnlit Battlefield becomes a 4/2 red and white Warrior creature with with “This creature has first strike as long as it's attacking” and “Whenever this creature attacks or blocks, torment yourself.” It's still a land. (To torment yourself, lose 3 life unless you discard a card or sacrifice a nonland permanent.)

Deadwood Grove enters tapped.
{T}: Add {B} or {G}.
{1}{B}{G}: Until end of turn, Deadwood Grove becomes a 2/3 black and green Horror creature with with deathtouch and “Whenever this creature attacks or blocks, torment yourself.” It's still a land. (To torment yourself, lose 3 life unless you discard a card or sacrifice a nonland permanent.)

This spell costs {2} less to cast for each creature that died this turn.
Flying, trample

Destroy target creature if it has the least power or is tied for least power among creatures on the battlefield.
Memento {3}{B}{B} (You may cast this from your graveyard for {3}{B}{B}. If you do, put it onto the battlefield transformed after it resolves. Exile it if it would leave the battlefield or not resolve.)