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.)

Shimmer (Whenever this creature attacks, create a tapped and attacking token that's a copy of it. Exile the token at the beginning of the end step.)
When Sandstrider enters, put a +1/+1 counter on target creature.

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.

Choose two —
• Target player creates a 3/3 green Wurm creature token.
• Target player puts three +1/+1 counters on a creature they control.
• Return target permanent card from your graveyard to your hand.
• Destroy target creature with flying.

When Sandwurm's Might enters, you may have target creature you control fight target creature you don't control.
Each creature you control enters with an additional +1/+1 counter on it.

Menace
Cycling {R} ({R}, Discard this card: Draw a card.)

Target creature gets -3/-3 until end of turn. You gain 3 life.

Flash (You may cast this spell any time you could cast an instant.)
When Sanguine Muralist enters, you may have target creature's toughness become 1 until end of turn.

Sanguine Oracle enters tapped.
{4}{B}, {T}, Sacrifice Sanguine Oracle: Target player discards two cards. Activate only as a sorcery.

{2}{B}: Return Sanitarium Skeleton from your graveyard to your hand.

Flash
Poisonous 2 (Whenever this creature deals combat damage to a player, that player gets two poison counters. A player with ten or more poison counters loses the game.)
When Sankataar Ambusher enters, if an opponent is poisoned, Sankataar Ambusher gets +2/+2 until end of turn.

Poisonous 3 (Whenever this creature deals combat damage to a player, that player gets three poison counters.)
When Sankataar Assailant enters, choose a counter on target permanent or player. Give that permanent or player another counter of that kind.

Poisonous 2 (Whenever this creature deals combat damage to a player, that player gets two poison counters.)
Sankataar Coilborn gets +1/+1 as long as an opponent is poisoned.

Poisonous 2 (Whenever this creature deals combat damage to a player, that player gets two poison counters.)
When Sankataar Scourge dies, if it attacked this turn, target opponent gets a poison counter.

Trample

{W}, {T}: Tap target creature.

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.

Create X 1/1 green Saproling creature tokens, then populate. (Create a token that's a copy of a creature token you control.)

When Sarrutu Worldbinder enters, create two 1/1 red Elemental creature tokens.
{1}{U}, {T}: Elementals you control gain flying until end of turn.
{2}{R}, {T}: Elementals you control get +2/+0 until end of turn.

At the beginning of your upkeep, you gain 1 life for each color among permanents you control.
{W}{U}{B}{R}{G}, Sacrifice Sartha's Studies: Double your life total.

When Sasori Nightrunner enters, create a 2/2 colorless Spirit creature token.
Whenever a colorless creature you control dies, each opponent loses 1 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.

When Satisfied Gleaner enters, you may search your library for a basic land card, put it onto the battlefield, then shuffle.