msem-instigator

Sage's Ashes enters tapped.
{T}, Sacrifice Sage's Ashes: Put target card from a graveyard on top of its owner's library.
{3}, Exile Sage's Ashes from your graveyard: Draw a card.

{T}: Add {C}.
{2}, {T}: Put target Aura or Equipment card from your graveyard on top of your library.

{3}: Create a 9/9 colorless Angel artifact creature token with flying and lifelink.

Storied spells you cast cost {1} less to cast. (Enchantments and legendary cards are storied.)

Hexproof

Haste
Sandstorm Sentinel enters with X +1/+1 counters on it, where X is your fealty to Deserts. (Each Desert you control counts toward your fealty to Deserts.)
Mirage {1}{R} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

When Sandswept Bazaar enters, you gain 2 life.
{T}: Add {C}.

{T}: Add {C}.
{5}, {T}, Sacrifice Sandswept Monument: Create a tapped 4/4 colorless Golem artifact creature token.

Trample

Flying, vigilance, lifelink
During each of your turns, you may cast a multicolored spell from your graveyard.

({T}: Add {U}.)
As Saturated Dunes enters, you may pay 1 life. If you don't, Saturated Dunes enters tapped.

Savage Lands enters tapped.
{T}: Add {B}, {R}, or {G}.

({T}: Add {G}.)
Savage Sanctuary enters tapped with two sanctum counters on it.
{T}, Remove a sanctum counter from Savage Sanctuary: Add {R} or {W}.

Creature spells you cast cost {2} less to cast.
Whenever a creature you control enters, if it doesn't have vanishing, put four time counters on it and it gains vanishing.

When Scabrous Automaton dies, draw a card, then add {C}{C}. Until end of turn, you don't lose this mana as steps and phases end.

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.

As Scorched Copse enters, you may tap an untapped creature you control. If you don't, Scorched Copse enters tapped.
{T}: Add {R} or {G}.

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

Scoured Barrens enters tapped.
When Scoured Barrens enters, you gain 1 life.
{T}: Add {W} or {B}.

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