msem-instigator

Flying, haste
Whenever Scourge of the Skies attacks, you may have it deal 5 damage to target creature.

As an additional cost to cast this spell, pay 3 life and sacrifice a creature.

Flying
Whenever you cast an instant or sorcery spell, Scourge of the Sun gets +1/+0 until end of turn. If you spent four or more mana to cast that spell, Scourge of the Sun gets an additional +1/+0 until end of turn.

Breach (Whenever this deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
At the beginning of your end step, discard a card. Then draw a card if an opponent is cursed.

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.)

Embellish {3}{B} (If you cast this spell for {3}{B}, create a 1/1 blue Thopter artifact creature token with flying when it enters.)
When Scrap Spiral enters, target creature gets -2/-2 until end of turn.
{3}{B}, {T}, Sacrifice an artifact: Target creature gets -2/-2 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

Flying
Dragon spells and Adventure spells you cast cost {1} less to cast.

When Scrapyard Aberration enters, you may sacrifice another artifact. If you do, target creature gets -2/-2 until end of turn.

Sacrifice Scrapyard Raiders: Target artifact gains indestructible until end of turn.

Flying
Whenever an artifact you control enters, you may activate one of its activated abilities without paying its cost.

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.)

{3}{B}, Exile Screeching Duneborn from your graveyard: You gain 1 life and draw a card.

When Scribal Puppeteer enters, create two 1/1 black Puppet creature tokens with “At the beginning of your upkeep, you lose 1 life.”

Trample, prowess

Ward {2}
Once each turn, if you would create one or more tokens, create that many of those tokens plus one instead.

Whenever you cast an instant or sorcery spell, put a +1/+1 counter on Scribe of the Sky Scrolls. If you spent four or more mana to cast that spell, Scribe of the Sky Scrolls gains flying until end of turn.

Whenever you cast a spell with mana value greater than Script Jockey's power, put a +1/+1 counter on Script Jockey.

Flying
Whenever you cast a creature spell, if Script Spirit is in your graveyard, you may have it become a copy of that spell until end of turn.

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Create two 1/1 white Human creature tokens.
II — Put a vigilance counter on target creature you control. It becomes a legendary God in addition to its other types.
III — Exile target creature an opponent controls that's a God or that has power 4 or greater.

When Scrivener of Sha'Iv enters, draw a card and adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)

When Scrollmaster dies, you may exile it. If you do, search your library for an instant or sorcery card with mana value 4 or less and cast it without paying its mana cost. If you searched your library this way, shuffle.

Scrollsnatcher can't block and can't be blocked.
Whenever Scrollsnatcher deals combat damage to a player, look at the top card of each library, then put any number of those cards into their owner's graveyards.