msem-instigator

Double strike
Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)
Whenever Sisters Suzakazi attacks, if you control another creature named Sisters Suzakazi, it deals 3 damage to any target.

Haste
Sixpod Sprinter can't be blocked except by creatures with flying or reach.

Trample
Skalnir, Ruinbringer enters with X +1/+1 counters on it.
When Skalnir, Ruinbringer enters, it deals damage equal to the number of +1/+1 counters on it to each creature without trample.

Skavi Behemoth can't be the target of nongreen spells or abilities from nongreen sources.

Resolute — Skerry Serpent must be blocked if able as long as its power is greater than its base power.

Whenever a player casts an instant or sorcery spell from their hand, you may exile that card as it resolves instead of putting it anywhere else.
Whenever Skill Sketcher attacks, you may cast a card exiled with it. That spell costs {X} less to cast, where X is Skill Sketcher's power.

Target creature gets -1/-1 until end of turn, a second target creature gets -2/-2 until end of turn, and a third target creature gets -3/-3 until end of turn.

When Skittering Atrocity enters, up to one target creature gets -X/-X until end of turn, where X is the number of Horrors you control.

Advance {3}{R}{R} (Cast this for {3}{R}{R} to advance it as it enters. {3}{R}{R}: Advance this as a sorcery.)
Flying, haste
Whenever Skiviar Scraplord advances, put a +1/+1 counter on it.

This spell can't be countered.
{U}: Exile Skulkling. Return it to the battlefield under its owner's control at the beginning of the next end step.
{1}{U}: Until end of turn, Skulkling gets +1/-1 and can't be blocked.
{3}{U}: Draw a card. Create a 1/1 blue Rogue creature token.

Creatures with power less than Skull-Crowned Chief's power can't block.

Flying
When Skymount Reinforcements enters, put a +1/+1 counter on another target creature.

Flying
As long as you control exactly one other creature, that creature gets +1/+1 and has flying.

Trample

Lifelink
When Slaffield Work-Hauler enters, create a 0/2 white Ox creature token for each enchantment you control.
Whenever an enchantment you control enters, Oxen you control get +1/+1 until end of turn.

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.

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

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.

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.)

Target player puts the bottom X cards of their library into their graveyard.

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.

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.

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.