msem-instigator

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

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 Shawlbinder enters, if you control a Desert, exile another target permanent. Return that card to the battlefield under its owner's control at the beginning of the next end step.

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

Revive—{B}, Discard a card. ({B}, Discard a card, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

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

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.

When Shifty Squirrel enters, you gain 3 life.
Sacrifice a creature: Transform Shifty Squirrel.

Whenever a creature you control dies, 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.”)
Whenever you sacrifice a noncreature permanent, each opponent loses 1 life and you gain 1 life.

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

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

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.)

Flying
When Shoal Raker enters, draw a card if an opponent is cursed.

Vanguard — Whenever a creature you control attacks alone, Shocking Ewe deals 2 damage to defending player.

When Shokan Captain enters, you may search your library for an Equipment card, reveal it, shuffle, then put that card on top.
Art of war — At the beginning of your end step, if Shokan Captain dealt damage to an opponent this turn, put a +1/+1 counter on it.

{2/W}{2/W}: Shrapnel Golem deals 3 damage to target creature blocking it.

Flying
Sacrifice a creature: Shrieking Nightwing gets +1/+1 until end of turn.

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.)

{T}: Add {C}.

When Silt Miner enters, you may salvage an artifact or creature card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

{T}: Untap another target nonland permanent. Activate only as a sorcery.

When Silver Gardener enters, create a 1/1 green Saproling creature token.
Unveil {2}{G}{W} ({2}{G}{W}: Transform this. Unveil only as a sorcery.)