msem-instigator

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

Add three mana of any one color.

Menace
When Scion of Calamities enters, exile the top two cards of your library. Until the end of your next turn, you may play one of those cards.
Whenever a Mountain you control enters, you may aetherize Scion of Calamities. (To aetherize, create a token that's a copy of it, then exile that token.)

Indestructible
Whenever a creature an opponent controls dies, put five +1/+1 counters on Scion of Death.

Deathtouch
When Scion of Desolation enters, put target creature card with mana value 3 or less from a graveyard onto the battlefield under your control.
Whenever a Swamp you control enters, you may aetherize Scion of Desolation. (To aetherize, create a token that's a copy of it, then exile that token.)

When Scion of Fecundity enters, search your library for a creature card with mana value 2 or less, reveal that card, put it into your hand, then shuffle.
Revive—{1}{G}{W}, Discard a card. ({1}{G}{W}, Discard a card, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

Trample
When Scion of Flourishing enters, put a +1/+1 counter on each other creature you control. Those creatures gain trample until end of turn.
Whenever a Forest you control enters, you may aetherize Scion of Flourishing. (To aetherize, create a token that's a copy of it, then exile that token.)

Poisonous 2 (Whenever this creature deals combat damage to a player, that player gets two poison counters.)
Snakes you control can't be blocked by creatures with power 2 or less.

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

Vigilance
When Scion of Storms enters, create a 2/2 white Elemental creature token with flying.
Whenever a Plains you control enters, you may aetherize Scion of Storms. (To aetherize, create a token that's a copy of it, then exile that token.)

Flying
When Scion of Torrents enters, you may return target nonland permanent to its owner's hand.
Whenever an Island you control enters, you may aetherize Scion of Torrents. (To aetherize, create a token that's a copy of it, then exile that token.)

First strike
Whenever Scion of the Pack enters or one or more creatures you control deal combat damage to an opponent or planeswalker, create a 2/2 green Hound creature token.

Scorch deals 3 damage to any target.

As Scorched Copse enters, you may tap an untapped creature you control. If you don't, Scorched Copse enters tapped.
{T}: Add {R} or {G}.

As an additional cost to cast Scorched-Earth Defence, reappropriate X times. (To reappropriate, exile exactly two cards from your hand and/or graveyard.)
Scorched-Earth Defence deals X damage to each creature and each planeswalker.

Flying, haste
Ride {1}{R} ({1}{R}: Transform this and attach it to target creature you control without a Mount. Ride only as a sorcery.)

Flying, haste
Whenever Scourge of the Skies attacks, you may have it deal 5 damage to target creature.

Flying
Whenever an artifact you control enters, you may activate one of its activated abilities without paying its cost.

When Screams from the Deep enters, exile up to one target monocolored permanent.
As long as an opponent owns three or more cards in exile, you may have Screams from the Deep assign its combat damage as though it weren't blocked.
Evoke {5} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Counter target permanent spell. (Then exile this card. You may cast the creature later from exile.)

Flying
Whenever you cast a creature spell, if Script Spirit is in your graveyard, you may have it become a copy of that spell until end of turn.

When Scrollmaster dies, you may exile it. If you do, search your library for an instant or sorcery card with mana value 4 or less and cast it without paying its mana cost. If you searched your library this way, shuffle.

Scrounging Dunes enters tapped.
{T}: Add {W} or {B}.
{1}{W}{B}: Until end of turn, Scrounging Dunes becomes a Wurm creature with lifelink in addition to its other types.
Scavenge {1}{W}{B}

At the beginning of your upkeep, you lose 1 life, then audition for black. (Create a 1/1 Construct Actor creature token, a Cleric Role giving 2/2 and lifelink, or a Warlock Role giving 2/1 and flying. Roles replace older ones.)

At the beginning of combat on your turn, if you cast both a creature spell and a noncreature spell this turn, untap up to one target land you control. It becomes a 3/1 red Sand creature with haste in addition to its other types until end of turn.