msem-instigator

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

Target player mills six cards. Return each creature that shares a name with a card milled this way to its owner's hand.
Prophecy {1}{U} (Once each turn, you may exile a card with prophecy as you reveal it. When you do, you may cast it for its prophecy cost as long as it's exiled.)

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

Solar Flare deals 3 damage to any target. You gain 3 life.

Destroy target artifact or enchantment. You gain 4 life.

Whenever Solemn Stag perseveres, put two +1/+1 counters on it. (A creature perseveres when it survives damage.)

As Soli Fortress enters, you may pay 1 life. If you don't, Soli Fortress enters tapped.
Satrapies you control have “{T}: Add {W}.”

(As an Encounter enters, choose an opponent to protect it. You and others can attack it. When defense counters are removed, create a 0/0 Army token if you don't control one, then put that many +1/+1 counters on a Army you control.)
When Soli Rising enters, reveal cards from the top of your library until you reveal a creature card. Put that card into your hand and the rest on the bottom of your library in a random order.

Tap all lands target player controls and that player loses all unspent mana.

Whenever Solvent Tide attacks, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)

({T}: Add {B} or {G}.)
Somber Marsh enters tapped.

When Somnambulance enters, each player conjures a card named Fatigue and puts it on top of their library. (It's a colorless sorcery that costs {2} with “Draw a card.”)
Whenever a player casts a spell named Fatigue, you may draw a card. If you do, you lose 1 life.

Enchant permanent
Enchanted permanent is a land with “{T}: Add {G}{W}{U}” and loses all other card types and abilities.
{1}, Discard Song of Shoals: Add one mana of any color. Scry 1.

Create a 4/4 red Dragon creature token with flying.
Showcase {5}{U}{R} (Then if you cast this for its showcase cost, create a 1/1 red Bard creature token that can't block and exile this. Whenever it attacks, you may cast a free copy of this.)

Creatures you control get +2/+2 and gain trample until end of turn.

Put three +1/+1 counters on target creature you control. It voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)

Defender, reach
When Soothevine Elemental enters, draw a card.

Equipped creature gets +1/+0 for each instant and sorcery card in your graveyard.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Menace
Inspired — Whenever Soul Engulfer becomes untapped, each opponent loses 4 life.

Choose one—
• Soul Flame deals X damage to target nonred creature.
• Target red creature gets +X/+0 until end of turn.

{1}, {T}: Exile target card from a graveyard. Scry 1.
{T}, Exile Soul Gate: Exile all graveyards.

When Soul Jar enters, exile target creature and each other creature with the same name as that creature until Soul Jar leaves the battlefield.

Destroy target creature unless its controller pays {3}.

Target creature gets -3/-3 until end of turn. You gain 3 life.

Enspirit (As you cast this spell, you may exile a nonenchantment creature you control until this leaves the battlefield or fails to resolve. Reduce this spell's cost by the exiled card's mana value.)
When Soul Trapper enters, tap target creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control Soul Trapper.