msem-instigator

Whenever you create one or more non-Mutant creature tokens, choose one —
• Create a 0/0 green Plant Mutant creature token, then put a +1/+1 counter on it for each of those non-Mutant tokens.
• Draw a card.

Whenever you pay a tithe, you may pay {2}. If you do, each opponent loses 3 life and you gain 3 life.

Target player sacrifices a creature.
Fabled {2}{B} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that player.)

Target player reveals a number of cards from their hand equal to the number of creature cards in your graveyard. You choose one of them. That player discards that card.

Whenever you attack, each opponent loses 3 life unless they discard a card or sacrifice a nonland permanent. Repeat this process once.
Fleeting {B}{R} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

Target creature gains trample and haste until end of turn. Harmonize. (Trigger up to one harmony of a permanent you control.)

Haste
At the beginning of combat on your turn, you may have target artifact or enchantment you control become a creature with base power and toughness X/X, where X is its mana value, in addition to its other types and gain haste until end of turn. (If it's attached to a permanent, it becomes unattached.)

At the beginning of each end step, if you gained life this turn, you get a glory counter. (You lose glory counters before life. A player with ten or more glory counters wins the game.)

{T}, Pay 1 life: Add {G}.
{8}{G}, Exile Singers' Grove from your hand: Creatures you control get +7/+7 until end of turn.

Whenever Single-Minded Mob becomes untapped, it gets +2/+2 until end of turn.

Whenever a storied permanent you control enters, each opponent loses 1 life and you gain 1 life. (Enchantments and legendary permanents are storied.)
{2}{B}{B}, Sacrifice Sinister Heir: Return target storied card from your graveyard to the battlefield.

Pay any amount of life. Look at twice that many cards from the top of your library and put one into your hand. Exile the rest.

Equipped creature gets +1/+0 and has menace.
Equip {2}

{T}, Sacrifice Sinister Thicket: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
{4}, Exile Sinister Thicket from your graveyard: Draw a card. Activate only as a sorcery.

Counter target spell.
Forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

Enchant creature
When Sink Beneath the Sands enters, target player loses 2 life and you gain 2 life.
Enchanted creature gets -4/-4.

Target creature gets -2/-2 until end of turn. Scry 1.

Mill a card. Target creature gets -X/-X until end of turn, where X is the number of cards put into your graveyard from anywhere this turn.

Enchant non-Army creature
When Sinking Pessimism enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.
Enchanted creature has “{4}: Untap this creature. If it untapped this way, put a stun counter on it.”

Return up to one target creature card from your graveyard to your hand, then exile all graveyards.

Target opponent reveals their hand. You choose a card from it. Exile that card. If a land card is exiled this way, its owner may conjure a card named Plains, Island, Swamp, Mountain, or Forest on top of their library.

This spell costs {1} less to cast for each poison counter your opponents have.
Poisonous 1 (Whenever this creature deals combat damage to a player, that player gets a poison counter. A player with ten or more poison counters loses the game.)
At the beginning of your end step, each opponent with seven or more poison counters loses the game.

Death knell — You gain 2 life. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)

Counter target spell. If you control a Wizard, scry 2. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Whenever Sir Roger Wimbledon deals combat damage to a player, you may put an exiled creature card you own into your hand.