msem-instigator

Whenever an opponent is dealt damage by one or more sources you control for the second time each turn, draw a card.

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.

Skin from Bone deals damage to target creature equal to your fealty to Mountains. (Each Mountain you control counts towards your fealty to Mountains.)

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.

Whenever another creature with mana value 2 or less you control enters, tap target creature an opponent controls.

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.

Flying
Spells you cast from anywhere other than your hand cost {2} less to cast.
Spells your opponents cast from anywhere other than their hand cost {2} more to cast.

Reach

Reach (This creature can block creatures with flying.)
Whenever a creature you control enters for the first time each turn, untap Skittering Swarm. It gets +1/+1 until end of turn.

Reach
Whenever another creature you control dies, surveil 1.
{T}, Sacrifice a non-Spider creature: Create a 1/2 green Spider creature with reach.

Whenever Skitterthorns blocks or becomes blocked, creatures you control gain deathtouch until end of turn.

Create a 1/1 green Squirrel creature token.
The next creature spell you cast this turn can be cast as though it had flash. As you cast that spell, it gains voracious 2. (As it enters, you may sacrifice up to two artifacts and/or creatures. That creature enters with that many +1/+1 counters on it.)

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.

Until end of turn, target creature you control gets +1/+1 and target creature an opponent controls gets -1/-1.

Skulking Claw can't be blocked by creatures with greater power.
Skulking Claw gets +1/+0 for each unblocked attacking creature you control.

{3}{W}: Tap target creature with power 4 or greater.

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.

{T}, Discard your hand: If two or more cards were discarded this way, search your library for a card and put that card into your hand, then shuffle.

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

Flying
Death knell — Skullhoarder Dragon gets +2/+0 until end of turn. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)

Creatures can't attack you unless their controller pays {2} for each of those creatures.
Whenever a permanent is returned to a player's hand, create a 1/1 white and blue Bird creature token with flying.

Sky-High Spires enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Flying
When Sky-Torrent Navigator enters, forebode. If you control two or more Pirates, forebode again. (To forebode, create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

Flying (This creature can't be blocked except by creatures with flying or reach.)
Whenever Skyblind Duo attacks, tap target creature defending player controls.

Equipped creature gets +2/+2.
Whenever equipped creature deals combat damage to a player, you may put a permanent card with mana value 2 or less from your hand onto the battlefield.
Equip {2}