msem-instigator

{T}: Add {U} or {R}.
{T}, Sacrifice Sigil of Ingenuity: Add {U}{R}.

{T}: Add {U} or {B}.
{T}, Sacrifice Sigil of Malice: Add {U}{B}.

{T}: Add {W} or {B}.
{T}, Sacrifice Sigil of Martyrdom: Add {W}{B}.

{T}: Add {R} or {G}.
{T}, Sacrifice Sigil of Savagery: Add {R}{G}.

{T}: Add {G} or {W}.
{T}, Sacrifice Sigil of Unity: Add {G}{W}.

Equipped creature has “{T}: Reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put it into your hand.”
Equip {2}

As long as Sigiled Scrollcase is attached to a creature you control, you have no maximum hand size.
Whenever equipped creature dies, draw a card.
Equip {1}

When Signet Ring enters, scry 1.
{2}, {T}, Sacrifice Signet Ring: Add two mana of different colors.

Silent Ridge enters tapped.
{T}: Add {B}.
Desertcycling {1}{B} ({1}{B}, Discard this card: Search your library for a Desert card, reveal it, and put it into your hand, then shuffle.)

{T}: Add {C}.

When Silt Miner enters, you may salvage an artifact or creature card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

Concord — Silt-Trench Brute gets +3/+3 and has trample as long as there are four or more card types among permanents you control.

{T}, Pay 1 life: Add {G}.
{8}{G}, Exile Singers' Grove from your hand: Creatures you control get +7/+7 until end of turn.

Equipped creature gets +1/+0 and has menace.
Equip {2}

Whenever Skeigr, Skhorvall Flagship attacks, it deals 3 damage divided as you choose among one, two, or three targets.
Crew 3 (Tap any number of creatures you control with total power 3 or greater: This Ship Vehicle becomes an artifact creature until end of turn.)

{T}, Sacrifice Skeletal Oasis: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

At the beginning of each upkeep, choose one or more —
• Untap target artifact.
• Untap target creature.
• Untap target land.

Equipped creature gets +0/+3 and has menace. (It can't be blocked except by two or more creatures.)
Equip {3}

{T}, Discard your hand: If two or more cards were discarded this way, search your library for a card and put that card into your hand, then shuffle.

Sky-High Spires enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Equipped creature gets +2/+2.
Whenever equipped creature deals combat damage to a player, you may put a permanent card with mana value 2 or less from your hand onto the battlefield.
Equip {2}

Skylight Fortress enters tapped.
When Skylight Fortress enters, you may search your library for a card named Skylight Fortress, reveal it, put it into your hand, then shuffle.
{T}: Add {C}.

Slaughterkeg can't attack or block.
While an opponent is choosing targets as part of casting a spell they control or activating an ability they control, that player must choose at least Slaughterkeg if able.
When Slaughterkeg dies, draw a card.

Identity — As long as you control at least two other creatures that share a creature type with Slicing Steer, Slicing Steer and creatures you control that share a creature type with it get +1/+0 and have menace.