msem-instigator

Put a +1/+1 counter on target creature. It gains hexproof until end of turn.

Return target nonland permanent to its owner's hand.
Inscribed creature gets +1/+1 and has flying.
Inscribe {3}{U} ({3}{U}: Exile this card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

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

{T}, Pay 1 life: Add one mana of any color. Spend this mana only to cast an instant or sorcery spell.

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.)

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.)

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.)

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.

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.

Flying
When Sigarda's Shepherd enters, another target creature you control gets +1/+1 and gains indestructible until end of turn.

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.)

{T}: Add {R} or {W}.
{T}, Sacrifice Sigil of Brutality: Add {R}{W}.

{T}: Add {G} or {U}.
{T}, Sacrifice Sigil of Creation: Add {G}{U}.

{T}: Add {B} or {R}.
{T}, Sacrifice Sigil of Destruction: Add {B}{R}.

{T}: Add {W} or {U}.
{T}, Sacrifice Sigil of Duty: Add {W}{U}.

Untap target creature. It gets +2/+2 until end of turn.
Cycling {W} ({W}, Discard this card: Draw a card.)