msem-instigator

Prowess
Each instant and sorcery card with mana value 3 or less in your hand has inscribe. The inscribe cost is equal to its mana cost increased by {1}{U/R}. (Pay that card's mana cost increased by {1}{U/R}: Exile that card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

When Shaidostan Cryoforger enters, exile the top card of your library.
When Shaidostan Cryoforger dies, you may put the exiled card into your hand.

As long as Shambling Morass is on the battlefield or in your graveyard, it's a land in addition to its other types.
When Shambling Morass dies, you may pay {1}. If you do, you draw a card and you lose 1 life.

Menace, lifelink
Whenever a creature enters under an opponent's control, you may have that player lose 1 life.

As long as it's your turn, Shell Merc has first strike and prowess.

When Sheltered Diviner enters, each player mills three cards.

You may look at the top card of your library any time.
{T}: Target player mills a card.

Shepherd of the People can't be blocked by creatures with power 2 or less.
Whenever another Citizen or Peasant you control enters, Shepherd of the People gets +1/+1 until end of turn.

Art of war — At the beginning of your end step, if Sheraku Elite dealt damage to an opponent this turn, put a +1/+1 counter on it.

Flying
When Shiftscale Drake enters, look at the top card of your library. You may put that card into your graveyard.

Whenever Shifty Fink attacks, if you have more cards in hand than defending player, it gets +2/+1 until end of turn.

Shimmering Seadragon gets +1/+0 and can't be blocked as long as you control a legendary creature.

Whenever you scry, put a +1/+1 counter on Shimmershell.

{T}: Add one mana of any color. Activate only if Shinrin Sage is enchanted, equipped, or has a card inscribed onto it.

Whenever you sacrifice a permanent, put a +1/+1 counter on Shipment Overseer.
Surpass {5}{R} ({5}{R}: Transform this creature. This costs {1} less to activate for each counter on it. Activate only as a sorcery.)

Whenever you cast a noncreature spell, Shiverpass Taskmage explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Marked creatures your opponents control lose all abilities.

Shrewd Sikoyo can't be blocked by creatures with power 4 or greater.
Shrewd Sikoyo gets +1/+0 as long as you have at least two more cards in hand than any opponent.

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Shrouded Cackler can't block.

Shu Qin enters with your choice of a flying or +1/+1 counter on him.
At the beginning of your upkeep, choose a creature in Shu Qin's pack. He gains that creature's abilities until end of turn. (Two or more creatures you control with equal power are in a pack.)

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Artifacts and creatures your opponents control enter tapped.

Flash
Harmony — Another target creature gets +1/+0 and gains indestructible until end of turn.
When Siamang Tale-Singer enters, harmonize. (Trigger up to one harmony of a permanent you control.)

Flash
Flying
Menagerie — Whenever Sigilwing Familiar deals combat damage to a player, if there are five or more creature types among creatures you control, draw a card.

When Silkweaver Matron enters, create a white Aura enchantment token named Spinning Silk attached to target creature. The token has enchant creature and “Whenever enchanted creature attacks, tap target creature defending player controls.”
{1}{W}: Untap target enchanted creature.