msem-instigator

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.)

Flying
{1}{R}: Sangrite Dragon gets +2/+0 until end of turn.
Sacrifice another creature: Add {R}{R}.

Trample
{2}{R}: Santriza Arsonist gets +3/+0 until end of turn.

Menace
When Santriza Gang-Boss enters, it deals X damage to any target, where X is the number of Pirates and/or Rogues you control.

Whenever you cast a noncreature spell, Sara, Entelan Elementalist gets +X/+0 until end of turn, where X is Sara's power. It deals 1 damage to each creature you don't control.

Whenever one or more creatures you control deal combat damage to a player, you may discard a card. If you do, draw a card.
{2}{R}, {T}, Exile two cards from your graveyard: Sarrutu Flamebinder deals 2 damage to any target.

Art of war — At the beginning of your end step, if Sasori Ronin dealt damage to an opponent this turn, it deals 1 damage to any target.

Flying
Tap five untapped Satrapies you control: Untap all creatures you control. After this main phase, there is an additional combat phase followed by an additional main phase. Activate only as a sorcery.

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Create a 1/1 red Satyr creature token with “This creature can't block.”
[Lore III] Creatures you control get +1/+0 until end of turn.

At the beginning of combat on your turn, if you control a creature with power greater than its base power, Satyr Trailblazer gets +2/+0 until end of turn.

Whenever Savage Companion and another creature attack, if Savage Companion doesn't have first strike, put a first strike counter on it.

Menace
Savage Stalker attacks each combat if able.

Whenever you cast a spell, if mana from an artifact was spent to cast it, exile the top card of your library. You may play that card until you exile another card with Savant of Cables.

Prowess
Whenever you cast a noncreature spell, you may choose target permanent with one or more time counters on it, then put a time counter on it or remove a time counter from it.

Whenever Savvy Saboteur attacks, target creature defending player controls can't block target creature you control this 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.

Defender
{T}: Scale-Crown Archer deals 1 damage to each opponent.
Prismatic — Whenever you cast a multicolored spell, untap Scale-Crown Archer.

{R}, Discard a card: Target creature blocking Scaled Mindreaver gains winnow until end of turn. (Damage dealt to it also causes its controller to lose that much life.)

Put a +1/+1 counter on target creature. That creature gains first strike until end of turn.
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.”)

Haste
When Scaled Thundercaller enters, target creature gains winnow until end of turn. (Damage dealt to it also causes its controller to lose that much life.)

When Scaleshredder enters, you may have it consume. If you do, reveal cards from the top of your library until you reveal a creature card. Put that card onto the battlefield and the rest on the bottom of your library in a random order. (To consume, sacrifice another creature or exile a creature card from your graveyard.)

Prowess
Whenever you cast a noncreature spell, create a 3/3 red Dragon creature token with flying.

Enchant player
Whenever enchanted player taps a nonbasic land they control, that land doesn't untap during its controller's next untap step.

Target creature you control gains haste until end of turn. Create a token that's a copy of that creature, then exile that token.

Haste
Motley — At the beginning of your upkeep, if there are five or more names among nonland permanents you control, Scarletblood Hound deals 3 damage to each opponent.