msem-instigator

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.

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.

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.

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.

Flying
When Skyborne Strategist enters, amass Soldiers 1. (Put a +1/+1 counter on an Army you control. It's also a Soldier. If you don't control one, create an 0/0 black Soldier Army creature token first.)

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}

Enchant creature
Enchanted creature gets +1/+1 and has flying.

Flying
Whenever Skyflock Warrior or another creature you control with flying attacks, create a 1/1 white Bird creature token with flying.

Flying
Cycling {U} ({U}, Discard this card: Draw a card.)

Flying
Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)
Your opponents can't cast spells during combat and can't activate abilities during combat unless they're mana abilities.