msem-instigator

Flying
Improve—{1}{B/R}, Sacrifice a creature. ({1}{B/R}, Sacrifice a creature: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Whenever another creature you control dies, each opponent loses 1 life and you gain 1 life. If that creature was sacrificed, instead each opponent loses 2 life and you gain 2 life.

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.

{3}{B}: You mill two cards. Each opponent loses 2 life.
{1}{G}: You may put a land card from your hand or graveyard onto the battlefield tapped.

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.

When Savannah Huntsman enters, it deals X damage to target creature or planeswalker, where X is the number of counters among permanents you control.

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.

When Scaleblight Warrior enters, you gain 2 life.
Pay 2 life: Scaleblight Warrior gains menace until end of turn.

{3}{G}: Scaled Devestator gets +1/+1 and gains trample until end of turn.

{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.)

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.)

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.

At the beginning of your end step, each opponent loses 1 life for each permanent they own that you control.

As Scavenging Sandwurm enters, choose decay or remain.
When Scavenging Sandwurm dies,
• Decay — Draw a card.
• Remain — Create a 2/2 black Zombie creature token.

Scavenging Soldier has first strike as long as it's attacking.
Attain {3}{W} ({3}{W}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

Scholar of the Staff can't block.
Inspired — Whenever Scholar of the Staff becomes untapped, up to one target creature can't block this turn.

Whenever one or more nontoken Merfolk you control attack, create a 2/1 red Merfolk creature token.

When Scion of Sarrithaz enters, create a 2/2 black Zombie creature token.
{2}{B}, Sacrifice a creature: Draw a card.

As Scion of Silence enters, choose a nonland card name.
Other permanents with the chosen name lose all abilities.

Sacrifice Scions of Old Jidai: Target player gains life equal to the life that player has lost this turn.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Scorchland Vandal attacks each combat if able.

Flash
When Scorned Arcanist enters, until end of turn if a creature would enter the battlefield, instead exile that creature and that creature's controller amasses Soldiers X, where X is that creature's mana value. (They put X +1/+1 counters on an Army they control. It's also a Soldier. If they don't control an Army, they create a 0/0 black Soldier Army creature token first.)

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