msem-instigator

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.

Flying
When Skystream Mantas is returned to your hand from the battlefield, draw two cards.

Rhapsody {3}{W}{W} (Pay {3}{W}{W} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
Players can't search libraries unless they pay {X}, where X is Skytouch Distorter's power.

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

Lifelink
When Slaffield Work-Hauler enters, create a 0/2 white Ox creature token for each enchantment you control.
Whenever an enchantment you control enters, Oxen you control get +1/+1 until end of turn.

Whenever Slaffield Workgate or another enchantment you control enters, create a 0/2 white Ox creature token.
{3}{W}: Return another target enchantment you control to its owner's hand.

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

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.)

Tribute 4 (As this creature enters, an opponent of your choice may put four +1/+1 counters on it.)
When Slaughter enters, if tribute was paid, destroy all other creatures. Otherwise, destroy all creatures you don't control.

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.

This spell costs {1}{B} less to cast if it targets a creature with indestructible.
Exile target creature.

Deathtouch, menace
Slayer of the Famed must be blocked each combat if able.

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

Enchant opponent
Whenever you attack enchanted player, look at the top X cards of your library, where X is one plus the number of attacking creatures you control. Put one of those cards into your hand and the rest on the bottom of your library in any order.

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

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.

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.

Ward {2}
Slippery Bunyip can't be blocked except by creatures with Adventures.

Slipsand Oasis enters tapped unless you played it from exile.
{T}: Add {W} or {B}.

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.)

Sludge-Gill Fox can't be blocked as long as it's attacking alone.
Whenever Sludge-Gill Fox deals combat damage to a player, you may draw a card.

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

Advance {5}{B}{B} (Cast this for {5}{B}{B} to advance it as it enters. {5}{B}{B}: Advance this as a sorcery.)
Whenever Sluiceway Collector advances, put a permanent card from a graveyard onto the battlefield under your control.

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.