msem-instigator

Sacrifice another creature: Put a +1/+1 counter on Skieryg Menace.

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

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.

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.)

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.

Survivors you control have flying.

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

Flying
When Skystream Mantas is returned to your hand from the battlefield, draw two cards.

Skysworn Aspirant has flying as long as it's embattled. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

Haste
Whenever a creature attacks, Slashing Pangolin gets +1/+1 until end of turn.

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.

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.

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.
Slipsand Expedition deals damage equal to the number of quest counters on it to any target.
Add {R}{R}{R}.

{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.

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.