msem-instigator

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.

When Shambling Retinue dies, create a 2/2 black Zombie creature token.

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

(Transcend as a sorcery to gain that type and a +1/+1 counter.)
Whenever a creature enters, its controller sacrifices another creature other than Shan Jun.
{W}{B}: Demigod — Exile each opponent's graveyard. Shan Jun gains protection from each name among cards exiled this way.
{6}{W}{B}: God — Target opponent creates a 1/1 white Avatar creature token with “When this creature dies, you lose the game.”

You may play Shanty Town from your graveyard as long as seven or more cards are in your graveyard.
Shanty Town enters tapped.
{T}: Add {W} or {B}.
Cycling {1}{W}{B} ({1}{W}{B}, Discard this card: Draw a card.)

Shapen's Cruelty deals 3 damage to any target.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Enchant creature
All creatures with power less than enchanted creature's toughness able to block enchanted creature do so.

Trample
Shapen, Spiteful Creation must be blocked each combat if able.
The first time Shapen, Spiteful Creation would be dealt damage each turn, prevent that damage.

You may have Shaper of the Formless enter as a copy of any creature on the battlefield, except it has “{2}{U}: Target face-down creature becomes a copy of this creature until end of turn. Turn that creature face up. At the beginning of the next cleanup step, turn it face down.”

When Shapur, the Fifth Shah enters, exile target instant or sorcery card from your graveyard. Until end of turn, you may cast that card. If that spell would be put into a graveyard, exile it instead.
Monument {4}{R} (You may cast this transformed from your graveyard for its monument cost. Exile it if it would leave the battlefield or not resolve.)

When Shara, Prime Geneticist enters, if X isn't 0, create two X/X green Mutant creature tokens.
[+1]: Surveil 2. At the beginning of your next end step, untap up to one permanent.
[–2]: Conjure a card named Test Run into your hand. (It's a sorcery that costs {X}{G} with “Create an X/X green Mutant creature token. Draw a card.”)
[–7]: Search your library for a card and put it into your hand. Repeat this process once for each token you control. Then shuffle.

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.”)

When you cast an instant or sorcery spell, you may sacrifice Shard Flower. If you do, copy that spell. You may choose new targets for the copy.

Equipped creature gets +1/+1 and has distorted. (It can be blocked by tapped creatures but not untapped creatures.)
Equip {1}

When Shardsong Seedling enters, conjure two cards named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

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

If one or more +1/+1 counters would be put on a creature you control, put that many +1/+1 counters on each creature you control instead.

{T}: Each player draws a card.

When Shark Slayer enters, you may destroy target creature with mana value less than or equal to the number of artifacts you control.

Flying
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Spell you cast cost {1} less to cast as long as it's not your turn.

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

Flying
When Sharp-Eyed Wingmate enters, you may return target creature to its owner's hand.

Frenzy 2 (Whenever this creature attacks and isn't blocked, it gets +2/+0 until end of turn.)

Lifelink
Each other artifact creature you control enters with an additional +1/+1 counter on it.