msem-instigator

Prowess
{1}: Shifting Dweller gets +1/-1 until end of turn.

Flying
When Shilgengar's Harvester enters, each opponent discards a card and loses 2 life.

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

Whenever Shina Taiyohata or another creature you control enters, you may have that creature gain haste. If you do, return that creature from the battlefield to its owner's hand at the beginning of the next end step.

Flash
When Shinrin Spellhunter enters, if an opponent cast a noncreature spell this turn, draw a card.

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.

Improve {1}{R} ({1}{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.)
When Siegebreaker Ogre enters, create two 1/1 red Goblin creature tokens with haste.

Prowess
{T}: Catalyze, then catalyze again. Activate only if Sigil Slinger's power is 5 or greater. (The next spell you cast this turn costs {2} less to cast.)

{T}: Scry 1.

Flying
When Silent Griffin enters, draw three cards, then put two cards from your hand on top of your library.

Flash (You may cast this spell any time you could cast an instant.)
When Silk Crane Adept enters, target creature gains hexproof until end of turn.

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.

Concord — Silt-Trench Brute gets +3/+3 and has trample as long as there are four or more card types among permanents you control.

{2}{U}, {T}: Look at the top card of your library. If it's a Scout card or a card with an Adventure, you may reveal it and draw a card.

Whenever you discard one or more cards, create a Treasure token and draw a card. This ability triggers only once each turn.
Whenever two or more creatures you control attack, you may discard a card. If you do, target creature can't block this turn.

Trample
Whenever Silver-Dawn Ranger becomes the target of a spell, put a +1/+1 counter on each Warrior you control.

First strike
Whenever Silverblade Cathar and at least two other creatures attack, draw a card.

When Silverhorn Battlemaster enters, put a +1/+1 counter on up to two target Warriors you control.
Whenever Silverhorn Battlemaster deals combat damage to a player, permutate. (You may remove a counter from a creature you control. If you do, put two +1/+1 counters on a different creature you control.)

Trample
Whenever Simian Sentinel attacks, it gets +X/+0 until end of turn, where X is the number of lore counters on Sagas you control.

First strike

At the beginning of each end step, if you gained life this turn, you get a glory counter. (You lose glory counters before life. A player with ten or more glory counters wins the game.)

Flying
Sire of Empires gets +1/+1 as long as you control another creature, has lifelink as long as you control an enchantment, and has vigilance as long as you control an artifact.

Menace
Whenever Skhorvall Warleader attacks, it gets +1/+0 until end of turn for each other attacking Warrior you control.

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.