msem-instigator

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.

When you unveil Shining Elementalist, creatures can't block this turn.

Flying, lifelink
Whenever Shioki, Imperial Heir attacks, exile any number of other target nonland permanents you control, then return those cards to the battlefield under their owner's control.

Equipped creature gets +2/+2 and has flying and lifelink.
When equipped creature deals combat damage to a player, unattach Shionoshio, Ocean's Vow, then transform it.
Equip {W}{U}
Shionoshio can be your commander.

Enchant creature you control
At the beginning of your upkeep, create a token that's a copy of enchanted creature.

Target creature gains hexproof until end of turn.
Monument {2}{U} (You may cast this transformed from your graveyard for its monument cost. Exile it if it would leave the battlefield or not resolve.)

Whenever Shoreline Stormers deals damage to a player, draw a card.
{2}{U}: Target creature can't be blocked this turn.

Search your library for two basic land cards, reveal them, put them into your hand, then shuffle. (Then exile this card. You may cast the creature later from exile.)

{2}{U}: Target creature can't be blocked this turn.

Shroudmaker's Domain enters tapped.
{T}: Add {W}.

Vigilance
Whenever Sibling of All Elements attacks, it gains flying until end of turn if you control a creature with flying. The same is true for first strike, double strike, deathtouch, indestructible, lifelink, menace, and trample.

Prevent all combat damage that would be dealt to Silent Reaver.
Prevent all combat damage Silent Reaver would deal to creatures.

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

{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.

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.)

Target player sacrifices a creature.
Fabled {2}{B} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that player.)

Whenever Sir Roger Wimbledon deals combat damage to a player, you may put an exiled creature card you own into your hand.

Destroy target nonland permanent with mana value 3 or less. (Then exile this card. You may cast Irbek later from exile.)

At the beginning of combat on your turn, target creature you control with flying gets +1/+1 until end of turn.

Whenever a creature dealt damage by Slave Child this turn dies, you may pay {B}. If you do, transform Slave Child.

Ward {2}
Slippery Bunyip can't be blocked except by creatures with Adventures.

Slipsand Oasis enters tapped unless you played it from exile.
{T}: Add {W} or {B}.

{T}: Target opponent loses 2 life. Activate only if you gained life this turn.

(Transform this if it's not attached to a creature. Pay {2}{W} as a sorcery to unattach it.)
Enchant creature you control
Slopestrider's Chariot's rider gets +1/+1 and has double strike.