msem-instigator

Vigilance, trample
When Threshold Guardian enters, return a creature you control to its owner's hand.

Target creature gets -3/-2 until end of turn.

Prismatic — Whenever you cast a multicolored spell, draw a card.

When The Dreadmoon Ascendancy enters, you may put two -1/-1 counters on target creature.
Whenever you put one or more counters on one or more other permanents, you may put a bale counter on The Dreadmoon Ascendancy.
{B}, Pay 1 life, Remove a bale counter from The Dreadmoon Ascendancy: Draw a card.

Whenever a creature you control enters for the second time each turn, you may put a +1/+1 counter on Warren Wardens.

Equipped creature gets +3/+2.
Equip enchantment creature {1}
Equip artifact creature {2}
Equip {3}

Archive X (As this enters, shuffle the top X cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
Whenever you draw a card from the archived library, create two 1/1 green Insect creature tokens.

Create two 1/1 blue Elemental creature tokens with flying.

Return target spell or creature to its owner's hand.
Quickdraw {U} (When a creature you control blocks or becomes blocked, you may cast this spell for {U}.)

At the beginning of combat on your turn, you may pay {2}{R}{R}. If you do, create a 4/4 red Dragon creature token with flying and haste. Exile that token at end of combat.
Ferocious — Whenever Xiusheng of the Dragon Realm attacks, if you control a creature with power 4 or greater, Xiusheng gains double strike until end of turn.

{T}, Pay 1 life: Add {R} or {W}.
{1}, {T}, Sacrifice Backstage Rooms: Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Defender
When Warden of Silence enters, draw a card.

{G}: Exile target card from a graveyard. If a creature card with flying is exiled this way, put a flying counter on Illustrious Qilin. The same is true for first strike, double strike, deathtouch, haste, hexproof, indestructible, lifelink, menace, reach, trample, and vigilance.

Ifram's Cavalier enters with two additional +1/+1 counters on it if you didn't cast it from your hand.

Gain control of target creature until end of turn. Untap it. It gains haste until end of turn.
Rerun (If you cast this from your hand, exile it as it resolves. Whenever a creature you control dies, you may cast this card from exile without paying its mana cost.)

{T}: Add {C}.
{3}, Exile Resurgent Oasis from your graveyard: Choose a basic land type. Create a tapped colorless land token that's a Desert and the chosen basic land type.

As an additional cost to cast this spell, discard a nonland card.
All creatures get -X/-X until end of turn, where X is the discarded card's mana value.

Flash
When Kaivilu, Ocean Warden enters, creatures your opponents control get -2/-2 and lose all abilities until end of turn.

Whenever you sacrifice one or more permanents, put a +1/+1 counter on Marsh Dweller.

Indestructible
Whenever a creature an opponent controls dies, put five +1/+1 counters on Scion of Death.

When Polgek Artisan enters, create an X/X colorless Juggernaut artifact creature token, where X is the number of artifacts and enchantments you control.

Haste, prowess
Wanderlust — When Spitfireling enters, if you control four or more differently named lands, create two 1/1 red Elemental creature tokens with prowess and haste.

You gain 7 life. (Then exile this card. You may cast the creature later from exile.)

Art of war — At the beginning of your end step, if Exultant Oni dealt damage to an opponent this turn, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)

Whenever Wild Bearmaster attacks, each other attacking creature you control gets +X/+X until end of turn, where X is Wild Bearmaster's power.