msem-instigator

When Stillmarsh Brinecatcher enters, return another target nonland permanent to its owner's hand.
At the beginning of your end step, if you control a permanent with mana value 5 or greater, you may sacrifice Stillmarsh Brinecatcher. If you do, draw a card and create a 3/2 colorless Horror creature token.

Menace
Whenever you discard a card, Stillsong Enforcer deals 1 damage to target opponent or planeswalker.

When Stilthorpe Falconer enters, create a 1/1 white Bird creature token with flying.

Whenever this creature or another Citizen or Peasant you control enters, you may exile target card from a graveyard. If you exile a creature card this way, you gain 1 life.

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

Whenever you cast a spell that doesn't share a color with Stinging Hunter, each opponent loses 1 life.

Stinging Swordfish has first strike as long as it's attacking.
When Stinging Swordfish dies, create an Equipment enchantment artifact token named Fish Sword with “Equipped creature gets +3/+1,” “Equipped creature has first strike as long as it's attacking,” and equip {2}. You may attach that token to a creature you control.

Flying
Whenever you cast your first spell each turn, add {U}{U}, {U}{R}, or {R}{R}.
Whenever you cast your second spell each turn, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
Whenever you cast your third spell each turn, Stirring Igmel deals 3 damage to each opponent.

Stoic Djinn has flying as long as it has a counter on it.

Double strike, vigilance, lifelink

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.

Haste
Storm Entity enters with a +1/+1 counter on it for each other spell cast this turn.

Whenever a permanent you control becomes tapped, Storm Servant gets +1/+1 until end of turn.

Stormbred Elemental gets +1/+1 as long as you control an Island.
{U}: Stormbred Elemental gains flying until end of turn.

Prowess, haste

Whenever one or more creatures you control deal combat damage to a player, exile a nonland card from that player's graveyard. Copy it. You may cast the copy. (You still pay its costs, including color. Copies of permanents enter as tokens.)

{1}, {T}: Surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)
{2}, {T}, Exile an instant or sorcery card from your graveyard: Stormvolt Apprentice deals 1 damage to each opponent.

Flash
Flying
When Strange Sights dies, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

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

Stray Sighthound can't be blocked by creatures with power 2 or less.
Attain {3}{G} ({3}{G}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

When Street Stalker enters, target opponent loses 1 life for each creature you control named Street Stalker.

Whenever you make first contact, target creature you control can't be blocked by Humans this turn. (You make first contact the first time each turn you cast a spell with a name not in your graveyard or control already.)

Harmony — Target creature gains haste until end of turn.
When Streetside Entertainer enters, harmonize. (Trigger up to one harmony of one permanent you control.)

Improve {1} ({1}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
At the beginning of combat on your turn, target creature you control with mana value 3 or less can't be blocked this turn. If Streetwise Investigator has two or more counters on it, that creature gains vigilance until end of turn.

Whenever Strict Instructor attacks, harmonize. (Trigger up to one harmony of a permanent you control.)
Harmony — Tap or untap another target permanent.