msem-instigator

({T}: Add {W} or {U}.)
Still Waters enters tapped unless you control two or more basic lands.

{1}, {T}, Sacrifice Stolen Strain: Target creature gains lifelink until end of tun.
{1}, {T}, Sacrifice Stolen Strain: Target creature gains winnow until end of turn. (Damage dealt to it also causes its controller to lose that much life.)

Flying
Tap an artifact you control, a creature you control, and an enchantment you control: Return Stonecut Lammasu from your graveyard to your hand. Activate only as a sorcery.

When Stonefall Golem leaves the battlefield, destroy target permanent.

Stonework Idol's power and toughness are each equal to the number of creatures you control.

At the beginning of your upkeep, if Stonework Infantry is on the battlefield, each player returns all cards named Stonework Infantry from their graveyard to the battlefield.

Whenever you cast an instant or sorcery spell, you may attach Stormbreaker's Edge to target creature you control.
Equipped creature gets +3/+0.
Equip {3}

Whenever equipped creature attacks, it deals damage to defending player equal to the number of instant and sorcery cards in your graveyard.
Equip {2}

Whenever one or more creatures you control attack, you may put a progress counter on Stormcannon Testing.
[PROGRESS 2-3] {T}: Target creature gets +2/+0 until end of turn.
[PROGRESS 4+] {T}: Target creature gets +2/+0 and gains double strike until end of turn.

{T}: Add {C}.
{T}, Exile two cards from your graveyard: Add {U} or {R}.

Stormcharged Pyre enters tapped unless you have two or more opponents.
{T}: Add {U} or {R}.

Other artifacts you control have ward {1}.
Overcast — Whenever you cast an artifact creature spell, if {C} was spent to cast it, it enters with an additional +1/+1 counter on it.

Strange Harbor enters tapped unless you have 15 or less life.
{T}: Add {U} or {R}.

Prowess
Pay 2 life: Change a target of target spell or ability to Straw Intellectual.

Creatures blocking or blocked by Straw Officer have wither. (They deal damage to creatures in the form of -1/-1 counters.)

As Straw Simulacrum enters, choose a creature type.
Straw Simulacrum is the chosen creature type in addition to its other types.
Other creatures you control of the chosen type get +1/+1.

Strider Engine enters tapped and with a -1/-1 counter on it unless you spent at least three colors of mana to cast it.

Equipped creature gets +1/+1 and has haste.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Stunning Cascade enters tapped.
{T}: Add {U} or {R}.
{2}{U}{R}, {T}, Sacrifice Stunning Cascade: Draw a card.

As Sturdy Outpost enters, you may pay 3 life. If you don't, it enters tapped.
{T}: Add {G}, {W}, or {U}.

({T}: Add {B}.)
As Stygian Dunes enters, you may pay 1 life. If you don't, Stygian Dunes enters tapped.

Substack Ports enters tapped.
{T}: Add {U} or {B}.
{U}{B}, {T}, Sacrifice Substack Ports: Conjure a card named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

{2}: Other creatures you control get +1/+0 until end of turn.
Whenever Sun-Crowned Flagship attacks, each attacking creature you control gains trample until end of turn.
Crew 7 (Tap any number of creatures you control with total power 7 or greater: This Vehicle becomes an artifact creature until end of turn.)

Sundappled Scrub enters tapped unless you control another Desert.
{T}: Add {G} or {W}.