msem-instigator

When Petal Scatterer enters, create a green Aura enchantment token named Blossom attached to target land. It has enchant land and “Enchanted land has ‘{T}: Add {G}{G}.'”
Petal Scatterer gets +1/+1 for each noncreature, nonland permanent you control.

Target creature gains flying and double strike until end of turn.
Flashback {2}{U}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

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.

Choose one—
• Destroy target artifact.
• Target creature gets +4/+4 until end of turn.

{2}{B}, Sacrifice a Clue: Target creature gets -3/-3 until end of turn.

Harness (You may tap a creature you control as you cast this spell. If you do, reduce this spell's mana cost by that creature's power.)
You gain X life.

{2}{B}, Sacrifice a creature: Manifest the bottom card of your library. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)
Whenever a creature you control is turned face up, it gains deathtouch until end of turn.

Create three 0/0 colorless Reflection creature tokens. Creature tokens you control get +2/+2 until end of turn.

Ravenous Hollow enters tapped.
{T}: Add {B} or {R}.
{2}{B}{R}: Until end of turn, Ravenous Hollow becomes a Wolf creature with first strike in addition to its other types.
Scavenge {2}{B}{R}

Untap target creature. It gets +1/+1 for each token you control until end of turn.

{T}: Target opponent loses 2 life. Activate only if you gained life this turn.

Search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.

{2}{G}: Target face-down creature you control becomes a Beast with base power and toughness 5/5 until end of turn.

Unending Slime enters with X +1/+1 counters on it.
{2}{G}{G}{G}: Return Unending Slime from your graveyard to your hand.

Unceasing Flames deals X damage to any target, where X is 2 plus the number of cards named Unceasing Flames in your graveyard.
Conjure three cards named Unceasing Flames and shuffle them into your main library.

Whenever you gain life, put a +1/+1 counter on Faithful Acolyte.
Faithful Acolyte has lifelink as long as it has four or more +1/+1 counters on it.

Codex — Unraveling; Unraveling; Unrelenting; Unrelenting; Mindrip; Swipe Secrets. (As this enters, conjure its contents into a shuffled face-up additional library.)
Flash
When Mei's Collection enters, draw a card from its codex.

When Black Cat dies, target opponent discards a card at random.

Once each turn, when a permanent is exiled from the battlefield by a spell or ability you control, you may draw a card.

Return target creature card with mana value 5 or less from your graveyard to the battlefield.
Metamorph {B} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up and cast it at any time for its metamorph cost.)

Voracious 2 (As this enters, you may sacrifice up to two artifacts and/or creatures. This creature enters with that many +1/+1 counters on it.)
When Opportunistic Beast enters, destroy up to one target creature that was dealt damage this turn.

Primal {2}{R}{R} (During your turn, you may cast this spell for {2}{R}{R} instead of playing a land.)
Flying, prowess
At the beginning of your end step, if you didn't cast a spell this turn, sacrifice Thunderstride.

Exile target instant or sorcery card from your graveyard. Copy it. You may cast the copy. (Cast a copy of this spell once while this creature is on the battlefield.)

Target creature you control gets +0/+3 and gains hexproof until end of turn.

When Night Shepherd enters, return a creature you control to its owner's hand.