msem-instigator

(Transform this if it's not attached to a creature. Pay {2}{B}{B} as a sorcery to unattach it.)
Enchant creature you control
Belmord Blood-Coach's rider gets +3/+3 and has deathtouch.
Whenever Belmord Blood-Coach's rider attacks, you may return target creature card with mana value less than its rider's power from your graveyard to the battlefield tapped.

Other Knights and Soldiers you control get +1/+0.
Cowards can't block Knights and Soldiers you control.
When Belmord Bloodcurdler enters, target creature an opponent controls becomes a Coward in addition to its other types. (This effect last indefinitely.)

Exile target nonland permanent. Its controller gains 5 life.

Bigroot Valley enters tapped.
{T}: Add {R} or {G}.
{1}, {T}: Add one mana of any color.

Legacy (You may play this side of this card only from your graveyard. Exile it if it would leave the battlefield or not resolve.)
Permanents you control have lifelink and “{T}: Add one mana of any color.”

Whenever you put one or more -1/-1 counters on a creature, create that many 1/1 black Faerie creature tokens with flying.

You lose 1 life and exile the top card of your library. You may repeat this process any number of times. Then put up to two cards exiled this way into your hand.
Coalesce {5}{B}{B} (You may cast this from your graveyard for {5}{B}{B}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Black Hole Musings's power is equal to the number of cards in exile.

Blazing Offerings deals 4 damage to target creature or planeswalker.

{1}{B}, {T}: Target creature gets +2/+2 and gains winnow until end of turn. (Damage dealt to it also causes its controller to lose that much life.)
{3}{B}{B}, {T}: Target creature gets -2/-2 and gains winnow until end of turn.

As an additional cost to cast this spell, sacrifice any number of creatures.
Target player loses 2 life for each creature sacrificed to cast Blood Lashing.

Improve {1}{R} ({1}{R}: 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.)
As long as Bloodbelly Glutton is embattled, it has first strike, menace, and haste. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Deathtouch
{T}, Sacrifice another creature: Add two mana of any one color.

You may have Blurry Counterpart enter as a copy of any creature on the battlefield.
Mirage {1}{U} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Whenever another creature you control dies, you may pay {1}. If you do, scry 1. (To scry 1, look at the top card of your library. You may put that card on the bottom of your library.)

Whenever Borsuppa Roughrider attacks, create a colorless Desert land token named Scoured Path with “{T}: Add {R}.” Sacrifice that token at the beginning of the next end step.

Whenever a creature with a counter on it dies, create a Gold token. (It's an artifact with “Sacrifice this artifact: Add one mana of any color.”)

Create an X/X green and blue Plant creature token, where X is the number of differently named lands you control.

Enchant creature
When Bramble Armor enters, put a +1/+1 counter on enchanted creature.
{G}, Sacrifice Bramble Armor: Enchanted creature gains indestructible end of turn. Tap it.

Enchant creature you control
When Brawnsurge enters, enchanted creature deals damage equal to its power to up to one target creature an opponent controls.
Enchanted creature gets +1/+1 and has trample.

Target player mills four cards, then mills an additional four cards for each Curse attached to them.

At the beginning of each opponent's upkeep, if that player has no cards in their hand, Cage of Torment deals 2 damage to that player.

Reach
Menagerie — When Canopyctopus enters, if there are five or more creature types among creatures you control, reveal the top card of your library. If its mana value is less than or equal to the number of lands you control, draw a card. Otherwise, you may put that card into your graveyard.

When Carrion Gourmet enters, each player sacrifices a creature.
Whenever another creature dies, put a +1/+1 counter on Carrion Gourmet.

Once each turn, when you sacrifice a permanent, you may put two progress counters on Ceaseless Research and surveil 2.
{2}{G}, Remove X progress counters from Ceaseless Research: Create an X/X green Mutant creature token. X can't be less than 3. Activate only as a sorcery.

Draw two cards.
Cycling {2} ({2}, Discard this card: Draw a card.)