msem-instigator

{R}, Discard a card: Target creature blocking Scaled Mindreaver gains winnow until end of turn. (Damage dealt to it also causes its controller to lose that much life.)

Put a +1/+1 counter on target creature. That creature gains first strike until end of turn.
Compose (Then if you cast this from your hand, exile it and create a Saga token with “r3—You may cast a copy of this card from exile without paying its mana cost.”)

Haste
When Scaled Thundercaller enters, target creature gains winnow until end of turn. (Damage dealt to it also causes its controller to lose that much life.)

When Scaleshredder enters, you may have it consume. If you do, reveal cards from the top of your library until you reveal a creature card. Put that card onto the battlefield and the rest on the bottom of your library in a random order. (To consume, sacrifice another creature or exile a creature card from your graveyard.)

When Scanning Module enters, crystallize. (Put a +1/+1 counter on a creature you control or create a Treasure.)
Equipped creature gets +1/+1.
Equip {1}

Remove a -1/-1 counter from target creature. That creature gets +2/+2 until end of turn.

Deathtouch
Inspired — Whenever Scar Tattooist becomes untapped, you may have target creature get -1/-1 until end of turn.

Advance {1}{B} (Cast this for {1}{B} to advance it as it enters. {1}{B}: Advance this as a sorcery.)
Whenever Scarcrawler advances, you lose life equal to its power, then put a +1/+1 counter on it.

Whenever Scarhide, Arsenal Crafter attacks, create a token that's a copy of an Equipment attached to Scarhide and attach the token to Scarhide. When you can't, arm it. (Create a colorless Equipment artifact token with “Equipped creature gets +1/+0” and equip {2}, then attach it to that creature.)

Prowess
When Scarlands Singularity enters, each player conjures a card named Data-Point into their hand. (It's a sorcery that costs {2} with “Draw a card.”)

Target creature you control gains haste until end of turn. Create a token that's a copy of that creature, then exile that token.

{2}{G}: Scarred Brawler gets +2/+2 until end of turn.

First strike
Disgraced 1 (This enters with a -1/-1 counter. Whenever it deals combat damage to a player, remove all -1/-1 counters from it.)

Choose one —
• Put a -1/-1 counter on target attacking or blocking creature.
• Scarring Censure deals 2 damage to target attacking or blocking creature.

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.)
Target creature gets -X/-X until end of turn.

Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.
Menagerie — If there are five or more creature types among creatures you control, scry 3.

Whenever Scathing Critics deals combat damage to a player or planeswalker, put a +1/+1 counter on it.

Scathing Review deals 2 damage to target creature. If you control an artifact, Scathing Review deals 2 damage to that creature's controller.

Target player reveals their hand. You choose a nonland card from it. That player discards that card. 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.”)

Put target creature on top of its owner's library. All other creatures that player controls get -2/-2 until end of turn.

Exile target creature. Return that card to the battlefield under its owner's control at the beginning of the next end step.

Target permanent you control gains hexproof and indestructible until end of turn. You gain 2 life.

Scavenger Holdout enters tapped.
When Scavenger Holdout enters, you may pay {3}. If you do, create two 1/1 green Scout creature tokens.
{T}: Add {C}.

Exile target creature with mana value 2 or less.