msem-instigator

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast a noncreature spell, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)

Discard a land card: Draw a card. Shardstorm Elemental gets +1/+0 and gains flying until end of turn. Activate only once each turn.

Flash
Unveil {3}{B}{G} ({3}{B}{G}: Transform this. Unveil only as a sorcery.)

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you casting a noncreature spell causes an ability of a creature you control to trigger, that creature gains your choice of first strike, haste, menace, or trample until end of turn.

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

Vigilance
Whenever one or more creatures you control deals combat damage to a player, you may discard a card. If you do, create a Function token with “Draw two cards.” (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)

Spells your opponents cast that target Sheltered Snowman cost {2} more to cast.
Whenever you cast a spell from exile, put a +1/+1 counter on Sheltered Snowman. It can't be blocked this turn.

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

Spirited (When this creature enters, you may activate one of its activated abilities without paying its cost.)
{2}{W}: Target creature gains vigilance until end of turn.

(Transcend as a sorcery to gain that type and a +1/+1 counter.)
Ward—Discard a card.
{B}{R}: Demigod — Draw a card, then discard a card. You may have each opponent sacrifice a nonland permanent with the same mana value as the discarded card.
{4}{B}{R}: God — Create two tokens that are copies of Shi Hou's back face.

Other creatures you control get +0/+1.
Whenever a creature you control perseveres, you gain 1 life. (A creature perseveres when it survives damage.)

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.

Trample
When Shigurei, the Floodbringer enters, up to three target permanents become colorless Island lands.

Shikai Revenant enters tapped.
At the beginning of your end step, if an opponent lost life this turn, you may return Shikai Revenant from your graveyard to your hand.

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.

Deception {U}{B} ({U}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Sacrifice a creature: Shinrei of the Ghosting Way can't be blocked this turn.
Whenever one or more Rogues you control deal combat damage to a player, return a creature card from your graveyard to your hand.

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

{8}{U}{U}: Monstrosity 5. (If this creature isn't monstrous, put five +1/+1 counters on it and it becomes monstrous.)
When Shipway Whale becomes monstrous, target player exiles all cards in their library, then shuffles their graveyard into their library.

Spells your opponents cast that target Shoalshine cost an additional {2} to cast.
Concord — {T}: Draw a card. Activate only if there are four or more card types among permanents you control.

When Shojiro, the Wavewaker enters, submerge up to eight target creatures your opponents control. (To submerge a card, exile it, then put it on the battlefield face down under its owner's control as a 2/2 creature.)

Shokan Battalion has double strike as long as it's enchanted, equipped, or has a card inscribed onto it.

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.)