msem-instigator

Sludge-Gill Fox can't be blocked as long as it's attacking alone.
Whenever Sludge-Gill Fox deals combat damage to a player, you may draw a card.

{2}, Remove a +1/+1 counter from a creature you control: Draw a card.

When Smuggler of the Santriza enters the battlefield, you may discard a card. If you do, draw a card.

({T}: Add {G} or {U}.)
Soaring Rainforest enters the battlefield tapped.
{1}, {T}: Add {G}{G} or {U}{U}.

({T}: Add {U} or {B}.)
Sodden Cavern enters the battlefield tapped.

When Sofia's Swashbucklers enters the battlefield, you may return target card with foretell from your graveyard to your hand.

Foretell {B}{R} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)
Haste
Whenever Sofia deals combat damage to an opponent, exile the top card of that player's library face down and look at it. You may play that card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast that spell. Then foretell Sofia. It costs {0} to foretell this way.

When Speaker of Open Waters enters the battlefield, create a green and white Aura enchantment token named Moray's Resolve attached to target creature you control. The token has enchant creature and “Enchanted creatures you control get +2/+2 and have trample and lifelink.”

Creatures your opponents control can't block alone. (They can block different creatures.)

This spell costs {1} less to cast for each other spell you've cast this turn.

Spellwoven Monster can't be the target of spells or abilities in any zone.
As you cast an instant or sorcery spell, reveal cards from the bottom of your library until you reveal an instant or sorcery card. You may add that card's effects to that spell. Then shuffle.

Shimmer (Whenever this creature attacks, create a tapped and attacking token that's a copy of it. Exile the token at the beginning of the end step.)

This spell costs {X} less to cast, where X is the number of cards types among cards in your graveyard.
Flying, ward {2}

({T}: Add {G}, {W}, or {U}.)
Stalwart Dominion enters the battlefield tapped.

({T}: Add {U} or {R}.)
Steamlit Peaks enters the battlefield tapped.
{1}, {T}: Add {U}{U} or {R}{R}.

Steel Hunter can't attack unless you control three or more other artifacts.

Cycling {2} ({2}, Discard this card: Draw a card.)

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

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.

Whenever you cast a spell, if it isn't your main phase, you may have Stoneshrine Guardian's base power and toughness become 4/1 or 1/4 until end of turn.

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 the battlefield as tokens.)

At the beginning of your upkeep, you may pay 2 life. If you do, exile the top card of target opponent's library. If a nonland card is exiled this way, copy it. You may cast the copy. (You still pay its costs, including color. Copies of permanents enter the battlefield as tokens.)

Concord — At the beginning of combat on your turn, if there are four or more card types among permanents you control, Sturdyshell Hammerclaw gets +2/+1 and gains trample until end of turn.

When Stygian Leviathan enters the battlefield, target opponent loses life equal to the number of Curses attached to them and you gain that much life.

First strike, vigilance
When Subnautical Legionnaire enters the battlefield, choose artifact, enchantment, or Merfolk. Exile target nonland permanent you don't control until you control no permanents of the chosen type.