msem-instigator

Trample, haste
Skullbriar gets +1/+1 for each creature card in all graveyards.
{T}: Add {B} or {G}.
Skullbriar, Death's Mockery remains transformed as it moves to any zone other than a player's hand or library.

Sky-High Spires enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Equipped creature gets +2/+2.
Whenever equipped creature deals combat damage to a player, you may put a permanent card with mana value 2 or less from your hand onto the battlefield.
Equip {2}

Skylight Fortress enters tapped.
When Skylight Fortress enters, you may search your library for a card named Skylight Fortress, reveal it, put it into your hand, then shuffle.
{T}: Add {C}.

Flying, trample, haste
Whenever a land you control enters or a land is put into your graveyard from the battlefield, Skyscreecher Dragon deals 2 damage to each opponent.

Trample

Whenever you tap a creature for mana, put a +1/+1 counter on that creature.
{T}: Add {G}.

As an additional cost to cast this spell, discard a card and sacrifice a nonland permanent.
Draw three cards.

Haste
Whenever a creature attacks, Slashing Pangolin gets +1/+1 until end of turn.

Vanguard — Whenever a creature you control attacks alone, target creature can't block this turn.

When Slaug's Warhowler enters, create a 1/1 red Goblin creature token with haste.
When Slaug's Warhowler dies, you may discard a card. If you do, draw a card.

Improve {1}{B/R} ({1}{B/R}: 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.)
At the beginning of each player's combat, you may have that player create two goaded 1/1 red Goblin creature tokens with haste. Exile those tokens at end of combat. (Until your next turn, they attack each combat if able and attack a player other than you if able.)

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Slaughtered Steps Taskmaster attacks, you may sacrifice another creature. If you do, Slaughtered Steps Taskmaster gets +2/+0 until end of turn.

Slaughterkeg can't attack or block.
While an opponent is choosing targets as part of casting a spell they control or activating an ability they control, that player must choose at least Slaughterkeg if able.
When Slaughterkeg dies, draw a card.

Slay Them in the Aisles deals 2 damage to each non-Actor creature.

Target creature blocks this turn if able. You may have it gain reach until end of turn.
Draw a card.

Whenever Sledgesuit Prospector attacks, choose any number —
• Sacrifice an artifact. If you do, put a +1/+1 counter on Sledgesuit Prospector.
• Discard a card. If you do, create a Treasure token.

Enchant land
Whenever enchanted land is tapped for mana, its controller adds {G}.
{G}, Sacrifice Sleeping Dryads: Draw a card.

You may change the targets of target instant spell, sorcery spell, or activated ability.

Create two 1/1 red and white Warrior creature tokens. Those tokens gain first strike until end of turn.

Identity — As long as you control at least two other creatures that share a creature type with Slicing Steer, Slicing Steer and creatures you control that share a creature type with it get +1/+0 and have menace.

Equipped creature has “{1}, {T}: This creature deals 1 damage to any target.”
Whenever equipped creature deals damage to a creature with power 5 or greater, sacrifice Sling of the Meek. If you do, destroy that creature.
Equip {3}

Slinking Raider can't be blocked by creatures with greater power.
Whenever Slinking Raider deals damage to a player or noncreature permanent, put a +1/+1 counter on it.
Surpass {5}{R} ({5}{R}: Transform this creature.
This costs {1} less to activate for each counter on it. Activate only as a sorcery.)

{1}{R}: Target creature can't block Slippery Salamander this turn.

(Add a quest counter as this enters. Sacrifice after 3.)
Once each turn, when you cast an instant or sorcery spell, you may add a quest counter.
1, 2 — Slipsand Expedition deals damage equal to the number of quest counters on it to any target.
3 — Add {R}{R}{R}.