msem-instigator

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

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.

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.

Whenever a creature dealt damage by Slave Child this turn dies, you may pay {B}. If you do, transform Slave Child.

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.

Flying, vigilance

Draw two cards.
Conjure a card named Fatigue and put it on top of your library. (It's a colorless sorcery that costs {2} with “Draw a card.”)

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

Choose target creature you control, then choose two —
• Put a +1/+1 counter on it.
• It gains hexproof until end of turn.
• It can't be blocked this turn.

Target player puts the bottom X cards of their library into their graveyard.

Until end of turn, target player can't cast noncreature spells, and that player can't activate abilities that aren't mana abilities.
Draw a card.

Vanguard — Whenever a creature you control attacks alone, it gets +1/+1 until end of turn. Untap that creature.

Put a +1/+1 counter on up to one target creature you control. That creature can't be blocked this turn.
Draw a card.

Flash
When Slippery Assassin enters, counter target spell if its mana value is less than or equal to Slippery Assassin's power.
Sacrifice another creature: Put a +1/+1 counter on Slippery Assassin.

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

Surveil 2. When you do, destroy up to one target creature with power less than or equal to the number of card types among cards in your graveyard.

{1}, {T}: Surveil 2.
{U}, {T}, Discard a card: Look at the top card of your library. If it's a nonland card, you may cast it. (You still pay its costs)

Whenever Slithering Eyes deals damage to a player, you may exile that many cards from the top of your library. Until the end of your next turn, you may play those cards.

Whenever a creature enters without counters during your next turn, you may put two +1/+1 counters on it. (Then exile this card. You may cast the creature later from exile.)

{2}, Remove a +1/+1 counter from a creature you control: Draw a card.

Distorted (This creature can be blocked by tapped creatures but not untapped creatures.)
{2}{B}, Sacrifice Sluiceway Shrieker: Put the bottom card of your library into your hand.

Defender
Whenever Slumbering Bear is dealt damage, put a +1/+1 counter on it.
Remove a +1/+1 counter from Slumbering Bear: It can attack as though it didn't have defender this turn.