msem-instigator

Improve {1}{B/R} ({1}{B/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.)
At the beginning of each player's combat, you may have that player create two goaded 1/1 red Goblin creature tokens with haste. Exile those tokens at end of combat. (Until your next turn, they attack each combat if able and attack a player other than you if able.)

Tribute 4 (As this creature enters, an opponent of your choice may put four +1/+1 counters on it.)
When Slaughter enters, if tribute was paid, destroy all other creatures. Otherwise, destroy all creatures you don't control.

Slay Them in the Aisles deals 2 damage to each non-Actor creature.

This spell costs {1}{B} less to cast if it targets a creature with indestructible.
Exile target creature.

Deathtouch, menace
Slayer of the Famed must be blocked each combat if able.

When Slayer's Grimoire enters, exile target non-Human creature an opponent controls until Slayer's Grimoire leaves the battlefield.
{2}{W}, {T}: You gain 2 life.

Return target instant or sorcery card from your graveyard to your hand.
Agonize (You may cast this card from your graveyard by putting a -1/-1 counter on a creature you control in addition to paying its other costs. Then exile this card.)

Prowess
Whenever you cast a noncreature spell, you may mill two cards.

Enchant opponent
Whenever you attack enchanted player, look at the top X cards of your library, where X is one plus the number of attacking creatures you control. Put one of those cards into your hand and the rest on the bottom of your library in any order.

Create two 1/1 red and white Warrior creature tokens. Those tokens gain first strike until end of turn.

Identity — As long as you control at least two other creatures that share a creature type with Slicing Steer, Slicing Steer and creatures you control that share a creature type with it get +1/+0 and have menace.

Flying
When Slighted Spirit enters, detain up to two target creatures. (Until your next turn, those permanents can't attack or block and their activated abilities can't be activated.)

Creatures your opponents control get -4/-0 until end of turn.
Quickdraw {1}{U}{U} (When a creature you control blocks or becomes blocked, you may cast this spell for {1}{U}{U}.)

Exile target creature you control, then return that card to the battlefield under its owner's control.
Draw a card.
Foretell {1}{U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Ward {2}
Slippery Bunyip can't be blocked except by creatures with Adventures.

Slippery Capuchin can't be blocked.
Whenever Slippery Capuchin becomes the target of a spell or ability, you may change the target of that spell or ability.

Whenever a creature attacks you or a planeswalker you control, that creature's controller mills two cards.

(Add a quest counter as this enters. Sacrifice after 3.)
Once each turn, when you cast an instant or sorcery spell, you may add a quest counter.
1, 2 — Slipsand Expedition deals damage equal to the number of quest counters on it to any target.
3 — Add {R}{R}{R}.

Menagerie — {1}{G}: Slipsand Hornshell gains indestructible until end of turn. Tap it. Activate only if there are five or more creature types among creatures you control.

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

Whenever you cast an instant, sorcery, or Wizard spell, Slipsand Runemage deals 1 damage to any target.

As long as there are four or more card types among cards in your graveyard, Slipstream Silencer can't be blocked.
Whenever Slipstream Silencer attacks, surveil 1.

Vanguard — Whenever a creature you control attacks alone, you may exile target instant or sorcery card from your graveyard. If you do, you may cast that spell from exile until your next turn. If that spell would be put into a graveyard, exile it instead.

Sludge-Gill Fox can't be blocked as long as it's attacking alone.
Whenever Sludge-Gill Fox deals combat damage to a player, you may draw a card.

Advance {5}{B}{B} (Cast this for {5}{B}{B} to advance it as it enters. {5}{B}{B}: Advance this as a sorcery.)
Whenever Sluiceway Collector advances, put a permanent card from a graveyard onto the battlefield under your control.