msem-instigator

{T}, Sacrifice an artifact or creature: Each opponent loses 1 life and you gain 1 life.

Menace
Whenever a creature you control deals combat damage to a player, exile the top card of that player's library. They lose life equal to that card's mana value.

Vigilance, ward {2}
{1}{G}, {T}: Put a +1/+1 counter on Dunetreader Tortoise. Activate only as a sorcery.

When Dusk Lieutenant enters, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)
Once each turn, when you discard a card during your turn, each opponent discards a card.

When this creature enters, create a Weapon token, then attach it to a creature you control. (It's an Equipment artifact token with equip {2} and “Equipped creature gets +1/+1”.)
Arise {5}{R} ({5}{R}, Exile this from your graveyard as a sorcery: Create a black token copy of it that's also a Zombie and can't block.)

{4}{G}{G}: Eager Voyager voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)
Whenever Eager Voyager phases in, if it has no +1/+1 counters on it, put four +1/+1 counters on it.

When Edina's Soulsinger enters, create a 1/1 blue Jellyfish enchantment creature token with slipstream. (It can't be blocked as long as only creatures with slipstream are attacking.)

Whenever you cast an artifact or enchantment spell, scry 1, then create a 1/1 white Merfolk creature token.
Whenever you cast a Merfolk spell, look at the top card of your library. If it's an artifact or enchantment card, you may reveal it and put it into your hand.

When Elder Prophesier enters, look at the top five cards of your library. You may reveal a Curse card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Emissary of Dai Gui enters tapped.
Emissary of Dai Gui doesn't untap during your untap step unless it's in a pack. (Two or more creatures you control with equal power are in a pack.)
Creature spells you cast cost {1} less to cast.

Flash
When Emissary of Dark Tides enters, you may return target noncreature spell or tapped creature to its owner's hand.

Whenever you cast a spell, draw X cards, where X is Enai, Who Wanders Alone's power.
As long as there are no other untapped creatures on the battlefield, Enai's power and toughness are switched.

{U}: Enduring Rockshell gets -1/+1 until end of turn.
Whenever Enduring Rockshell perseveres, draw a card, then discard a card. (A creature perseveres when it survives damage.)

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Scry 1.
[Lore III] Target creature you control can't be blocked until end of turn.

{T}: Envious Nereid deals 1 damage to target creature and 1 damage to that creature's controller.

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Until your next turn, target creature an opponent controls gets -1/-0.
[Lore III] Scry 2, then draw a card.

Embellish {6}{U} (If you cast this spell for {6}{U}, create a 1/1 blue Thopter artifact creature token with flying when it enters.)
Whenever you attack, return any number of nonland permanents with different controllers and mana value less than or equal to the number of artifacts you control to their owners' hands.

When Fabled Chishou enters, create a token that's a copy of it, except it doesn't have this ability.
At the beginning of each end step, if Fabled Chishou isn't in a pack, sacrifice it. (Two or more creatures you control with equal power are in a pack.)

When Faithless Deserter enters, you may sacrifice a creature. If you do, each opponent sacrifices a creature.

When False-Cure Smuggler enters, put a -1/-1 counter on another target creature.
{1}{U}, Sacrifice a creature: Proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

Whenever Fated Mariner attacks, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)
{1}{U}: Fated Mariner can't be blocked this turn.

{T}: Draw a card. Activate only if you created a token this turn.

Menace
When Fenhauler Gang enters, each player mills three cards.
Whenever Fenhauler Gang deals combat damage to a player, return up to one target creature or land card from your graveyard to your hand.

Deathtouch
Infiltrate (Whenever one or more attacking creatures you control aren't blocked, this creature gets +1/+1 until end of turn.)

Whenever Ferris, the Sapphire Storm or another creature you control enters, each opponent mills X cards, where X is that creature's power.