msem-instigator

Return up to one target creature to its owner's hand. If you do, that player discards a card at random.
Coalesce {5}{U}{B} (You may cast this from your graveyard for {5}{U}{B}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Whenever Shroud the World in Doom deals combat damage to an opponent, that player discards a card at random.

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Shrouded Cackler can't block.

Enchant creature
When Shrouded Spoils enters, draw two cards.
Enchanted creature can't be blocked.

This spell costs {2} less to cast for each face-down creature you control.
Flying

Shu Qin enters with your choice of a flying or +1/+1 counter on him.
At the beginning of your upkeep, choose a creature in Shu Qin's pack. He gains that creature's abilities until end of turn. (Two or more creatures you control with equal power are in a pack.)

Create a 1/1 black Spirit creature token with flying for each creature card and Revelation card in your graveyard.
Coalesce {6}{G}{W}{U} (You may cast this from your graveyard for {6}{G}{W}{U}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Draw a card. If this is the third spell you've cast this turn, create a 2/2 blue Drake creature token with flying. If this is the sixth spell you've cast this turn, exile it, then return up to three target instant and/or sorcery cards from your graveyard to your hand and untap up to six lands.

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Artifacts and creatures your opponents control enter tapped.

Vigilance
Shuye, Forever Watching's power and toughness are each equal to the number of noncreature permanents you don't control.

When Siamang Minstrel enters, you may put a lore counter on target Saga you control.

Flash
Harmony — Another target creature gets +1/+0 and gains indestructible until end of turn.
When Siamang Tale-Singer enters, harmonize. (Trigger up to one harmony of a permanent you control.)

At the beginning of your upkeep, you lose life equal to the number of Armies you control, then recruit. (Create a 0/0 white Soldier Army creature token, then put a +1/+1 counter on each Army you control.)

Vigilance
Whenever Sibling of All Elements attacks, it gains flying until end of turn if you control a creature with flying. The same is true for first strike, double strike, deathtouch, indestructible, lifelink, menace, and trample.

Enchant creature
Enchanted creature gets +1/+0 and has deathtouch.
When Sickening Madness is put into a graveyard from the battlefield, draw a card.

Siege Ent can't be blocked by creatures with power 2 or less as long as it's embattled. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

Gain control of target nonland permanent an opponent controls. Its owner reveals cards from the top of their library until they reveal a card that shares a type with that permanent, then puts it onto the battlefield and shuffles.

Improve {1}{R} ({1}{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.)
When Siegebreaker Ogre enters, create two 1/1 red Goblin creature tokens with haste.

Deathtouch
When Siesa Tremund enters, for each player, search that player's library for a card and exile it. That player shuffles. You may play those cards for as long as they remain exiled, and you may spend mana as though it were mana of any type to cast those spells.

Flash
Whenever you cast Siflir, Elder Pawn or another spell, if you paid an alternate or additional cost to cast it, draw a card.
Wander {3}{U}{U} (You may cast this from the battlefield for its wander cost.)

Draw three cards, then discard a card unless you've catalyzed three or more times this turn.

When Sift Through False Leads enters, exile the top five cards of your library, then investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
{2}, Sacrifice a Clue: Put a card exiled with Sift Through False Leads into your hand.

First strike
Whenever Sighted-Caste Knight deals combat damage to a player, draw a card.

Revive {3}{B} ({3}{B}, 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.)

When Sights Beyond enters, scry 3.
Concord — At the beginning of your upkeep, if there are four or more card types among permanents you control, draw a card.

Prowess
{T}: Catalyze, then catalyze again. Activate only if Sigil Slinger's power is 5 or greater. (The next spell you cast this turn costs {2} less to cast.)