msem-instigator

Trample
Savage Mammoth gets +1/+1 for each land you control.
Ride {4}{G} ({4}{G}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

Target creature gets +3/+3 and gains trample until end of turn.

(Transform this if it's not attached to a creature. Pay {1}{R} as a sorcery to unattach it.)
Enchant creature you control
Scale Bearer's rider gets +4/+3 and has flying and haste.
Whenever Scale Bearer's rider attacks, you may pay {2}{R}. If you do, it deals damage equal to its power to target creature or planeswalker.

Deathtouch
Whenever Scaleblight Bokor attacks, it gets +1/+1 until end of turn for each Curse attached to defending player.

Enchant player
When Scaleblight's Quarry enters the battlefield, you may have target creature you control deal damage equal to its power to target creature enchanted player controls.
Whenever enchanted player becomes the target of a spell you control, you gain 1 life.

Whenever Scavenger of the Old Bay deals combat damage to a player, draw a card.
Ride {1}{U} ({1}{U}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

{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.)

Flying
Whenever Scavenging Hilakites attacks, you may sacrifice another creature. When you do, Scavenging Hilakites deals damage equal to the sacrificed creature's power to any target.

Scion of Belmord has lifelink as long as it's embattled. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

Flying
Civilized — Scion of Sannuria has vigilance as long as you control an artifact, a creature, and an enchantment.

Vigilance
Other Knights and Soldiers you control get +1/+1.
{2}{B}, {T}, Sacrifice a Knight or Soldier: Destroy target creature or planeswalker. Activate only as a sorcery.

Counter target spell with no subtypes. Surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)

When Scorpid Sniper enters the battlefield, you may have target creature get -1/-1 until end of turn.

Scoured Mesa enters the battlefield 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.)

Flying, haste
Ride {1}{R} ({1}{R}: Transform this and attach it to target creature you control without a Mount. Ride only as a sorcery.)

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.)

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

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.

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.

{3}{G}: Seasoned Farmer gets +2/+2 until end of turn.

As Secluded Courtyard enters the battlefield, 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 or creature card of the chosen type.

This spell can't be countered.
Draw a card.
Reprise {2}{U} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)

Scry 2, then draw two cards. (Look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

(Add a quest counter as this enters. Sacrifice after 3.)
Whenever a land enters the battlefield under your control, add a quest counter.
1, 2 — Create a 1/1 Scout creature token that's all colors.
3 — Creatures you control get +2/+1 until end of turn.

Flash
Flying
When Seeker Amalgam enters the battlefield, you may counter target spell with mana value less than or equal to the number of Elementals you control.