msem-instigator

Return target creature to its owner's hand. If you controlled that creature, draw a card.

Prevent all combat damage that would be dealt to Silent Reaver.
Prevent all combat damage Silent Reaver would deal to creatures.

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.)

Return target creature card from your graveyard to your hand.
Compose (Then if you cast this from your hand, exile it and create a Saga token with “r3—You may cast a copy of this card from exile without paying its mana cost.”)

Non-Avatar creatures can't attack you or planeswalkers you control unless their controller pays {2} for each of those creatures.

Flash
You may cast cryptic spells as though they had flash. (Artifacts, enchantments, and modal spells are cryptic.)

Flash (You may cast this spell any time you could cast an instant.)
When Silk Crane Adept enters, target creature gains hexproof until end of turn.

Reach

When Silkweaver Matron enters, create a white Aura enchantment token named Spinning Silk attached to target creature. The token has enchant creature and “Whenever enchanted creature attacks, tap target creature defending player controls.”
{1}{W}: Untap target enchanted creature.

{2}, Pay 2 life: Silkwrap Brawler gains indestructible until end of turn.

{T}: Add {C}.

Whenever Silt Lurker deals combat damage to a player, mill three cards, then draw a card if seven or more cards are in your graveyard.
Cycling {G} ({G}, Discard this card: Draw a card.)

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}: Untap another target nonland permanent. Activate only as a sorcery.

(Add a quest counter as this enters. Sacrifice after 3.)
Whenever you cast your first spell outside your main phase each turn, add a quest counter.
1, 2 — Draw cards equal to the number of quest counters on Siltbottom Expedition, then discard that many cards.
3 — Put up to two target instant or sorcery cards from your graveyard on top of your library in any order, then draw a card.

Whenever Siltbottom Freebooters attacks, target Pirate gains menace until end of turn.

{2}{U}, {T}: Look at the top card of your library. If it's a Scout card or a card with an Adventure, you may reveal it and draw a card.

{2}{B/G}: Return Silthway Scuttler from your graveyard to your hand.
{2}{B/G}, Exile Silthway Scuttler from your graveyard: Put two +1/+1 counters on target creature.

Desecrate (When this creature enters, you may sacrifice an artifact or land.)
When Siltsplitter desecrates a permanent, each opponent sacrifices an artifact.

When Silver Gardener enters, create a 1/1 green Saproling creature token.
Unveil {2}{G}{W} ({2}{G}{W}: Transform this. Unveil only as a sorcery.)

First strike
Whenever Silverblade Cathar and at least two other creatures attack, draw a card.

Whenever you draw a card, Silverblood Aspirant gets +1/+1 until end of turn.
{1}{R}, Discard a card: Draw a card.

When Silvercrest Historian enters, scry 1, then investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)