msem-instigator

Siphon (Each -1/-1 counter you put on your creatures up to their remaining toughness while casting this pays for {1}.)
Search your library for up to two Forest cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Gain control of target permanent. (Cast a copy of this spell once while this creature is on the battlefield.)

When Backstage Broken enters, create a 1/1 colorless Construct Actor creature token.
Whenever a token you control leaves the battlefield, you gain 1 life.

Whenever Doomsower or another Human you control dies, you draw a card and you lose life equal to that creature's power.

Menace
When OM-6 Walker dies, OM-6 Walker deals damage to each player equal to twice the number of nonbasic lands that player controls.

Source Decay deals 2 damage to each opponent. Create two 1/1 colorless Servo artifact creature tokens.
Whenever a creature you control deals combat damage to a player, you may pay {2}{B}{R} and sacrifice it. If you do, return Source Decay from your graveyard to your hand.

Target opponent discards a card. If they can't, draw a card. (Then exile this card. You may cast the creature later from exile.)

{T}, Sacrifice an artifact: Add {R}{R}{R}.

{B}, {T}, Sacrifice a creature: Draw a card. If that creature had flying, put a flying counter on a creature you control. The same is true for first strike, double strike, deathtouch, haste, hexproof, indestructible, lifelink, menace, reach, trample, and vigilance.

Flying, deathtouch
Whenever you cast an instant or sorcery spell, return target creature card from your graveyard to the battlefield.

When this creature enters, put a -1/-1 counter on a creature you control.
{2}{U}, {T}: For each permanent, you may give it a counter of a kind already there. Then draw a card for each permanent with three or more counters on it.

When Over the Horizon enters, scry 1.
{T}: Add {C}.
{1}, {T}: Return Over the Horizon to its owner's hand.

When Palace Vanguard enters, choose one —
• Create a 1/1 blue Bird creature token with flying.
• Create a 2/2 white Cat creature token.

When Kinsang Butcher enters, create a Treasure token.
{1}, Sacrifice an artifact or another creature: Put a +1/+1 counter on Kinsang Butcher. Activate only as a sorcery.

Pressure {U}{U} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Counter target spell.

Infiltrate (Whenever one or more attacking creatures you control aren't blocked, this creature gets +1/+1 until end of turn.)
Other creatures you control have infiltrate.

As Nimble Sandstorm enters, choose speed or power.
At the beginning of combat on your turn,
• Speed — Target creature gains haste until end of turn.
• Power — Target creature gets +2/+0 until end of turn.

Destroy target creature with power 4 or greater.
Create two Idol tokens. (They're artifacts with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)

Kicker {X} (You may pay an additional {X} as you cast this spell.)
When Korrinary Warcaller enters, if it was kicked, search your library for a Rebel permanent card with mana value X or less, put it onto the battlefield, then shuffle.

Calamitous Rampage deals 5 damage to any target.
Cycling {G} ({G}, Discard this card: Draw a card.)

Flying
{1}{B}, {T}: Destroy target creature that was dealt damage this turn.

Counter target spell. Tap all lands that spell's controller controls and that player loses all unspent mana.

Bleed {2}{U} (You may cast this spell for its bleed cost if an opponent has lost life this turn.)
Put target creature on top of its owner's library.

Whenever you cast a Knight spell or an Adventure spell, Wimbledon's Squire gets +1/+1 until end of turn.

Vigilance
If another creature would die, exile it instead.
At the beginning of your upkeep, return each creature card exiled with Arbiter of Endless Summer to the battlefield under its owner's control.