msem-instigator

Equipped creature gets +1/+1.
Equipped creature has “When this creature dies, if it's not a token, create a token that's a copy of it except it's a colorless Spirit Dragon with flying in addition to its other abilities.”
Equip {2}

When Scanning Module enters, crystallize. (Put a +1/+1 counter on a creature you control or create a Treasure.)
Equipped creature gets +1/+1.
Equip {1}

Scavenger Holdout enters tapped.
When Scavenger Holdout enters, you may pay {3}. If you do, create two 1/1 green Scout creature tokens.
{T}: Add {C}.

{3}, {T}: Draw a card.
Crew 3 (Tap any number of creatures you control with total power 3 or greater: This Vehicle becomes an artifact creature until end of turn.)

Crew 1 (Tap any number of creatures you control with total power 1 or greater: This Vehicle becomes an artifact creature until end of turn.)
Whenever Scavengermobile deals combat damage to a player, choose land or nonland, then rediscover a card of that kind. (Look at the top card of your library. You may reveal it and put it into your hand if it's a card of the chosen type. Otherwise, put it back or into your graveyard.)

When Scintillating Tome enters, choose a nonbasic card name.
{T}: Scry 1, then you may reveal the top card of your library. If a card with the chosen name is revealed this way, put it into your hand.

Equipped creature gets +2/+2.
{1}: Attach Scoundrel's Aetherlock to target Rogue.
Equip {2}

Menace
Sacrifice another artifact: Scrap Buggy becomes an artifact creature until end of turn.
Crew 2 (Tap any number of creatures you control with total power 2 or greater: This Vehicle becomes an artifact creature until end of turn.)

Scrap, the Second Myr has all activated abilities of other artifact creatures you control.

When Scrapgear Contraption dies, you may put a +1/+1 counter on target creature.

Vigilance, trample

When Screams from the Deep enters, exile up to one target monocolored permanent.
As long as an opponent owns three or more cards in exile, you may have Screams from the Deep assign its combat damage as though it weren't blocked.
Evoke {5} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

When Scrying Pool enters, scry 2.
{1}, {T}: Add one mana of any color.

{T}: Add {C}.
{T}, Tap an untapped artifact, creature, or land you control: Add one mana of any color.
{T}: Choose a card name, then reveal the top card of your library. If that card has the chosen name, you may sacrifice Sealed Archives and draw a card.

Cards in graveyards lose all abilities.
Cards in graveyards can't be the target of spells or abilities.

When Sealed Riftway enters, exile up to one target card from a graveyard.
{2}, {T}, Sacrifice Sealed Riftway: Exile target player's graveyard. Draw a card.

{T}: Add one mana of any color.
{2}, {T}: Draw a card. Activate only if you sacrificed a permanent or discarded a card this turn.

As Secluded Courtyard enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type or activate an ability of a creature source of the chosen type.

When Secluded Monument enters, choose a color.
Whenever you cast a spell of the chosen color, Secluded Monument becomes a 5/5 Golem creature until end of turn.

When Seductive Seashell enters, target player mills two cards.
{2}, Sacrifice Seductive Seashell: Target player mills four cards.

Equipped creature has hexproof and distorted. (It can be blocked by tapped creatures but not untapped creatures.)
Equip {1}

When Seeker's Guardian enters, reveal the top card of your library.

Equipped creature gets +1/+1.
At the beginning of your end step, if you don't control a creature, create a 1/1 white Human creature token and attach Seeking Sword to it.
Equip {1}

{3}, {T}: Scry 3.
{5}, {T}: Fateseal 3.
{7}, {T}: Draw two cards.

{T}: Add {C}.
{7}, {T}: Create a 2/2 colorless Spirit creature token.