msem-instigator

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever a marked creature dies, you lose 1 life and you draw a card.

Return target creature or planeswalker card from your graveyard to the battlefield. If that card was a creature, it's an Actor in addition to its other types.

Whenever a creature enters this turn, destroy it.

Investigate, then target creature gets -1/-1 until end of turn for each Clue you control. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

{0}: Until end of turn, Eldritch Egg becomes a copy of target permanent card in a graveyard with mana value 6 or less except it's an artifact. Activate only once each turn. (It has no other card types.)

Destroy target creature. You may remove a counter from up to one target permanent.

Flying
Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever a marked creature dies, you gain 2 life.

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards.

Choose two —
• You gain 3 life.
• Lost Memories deals 3 damage to any target.
• Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever a marked creature dies, put a +1/+1 counter on Mei's Collector.

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I, II — Each player discards a card or sacrifices a creature.
III — Each opponent loses life equal to the number of creature cards in their graveyard. You gain life equal to the number of creature cards in your graveyard.

Target creature gets -2/-2 and is marked until end of turn.

Whenever a creature dealt damage by Slave Child this turn dies, you may pay {B}. If you do, transform Slave Child.

Menace

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.)
Slums Thug gets +1/+1 and has menace as long as you've gained life this turn.

When Street Stalker enters, target opponent loses 1 life for each creature you control named Street Stalker.

Once each turn, when you search your library, you may add {B}{B}.

Whenever a creature dealt damage by Truth Extractor this turn dies, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Undercity Diplomat can't be blocked by marked creatures.

At the beginning of your upkeep, reveal the top card of your library. If it has the same name as a card in your graveyard, put the revealed card into your hand. Otherwise, put it into your graveyard.

All creatures have “When this creature enters, destroy target creature with a lesser mana value.”

{4}{B}{B}: Return Urchin Defector from your graveyard to the battlefield transformed.

Whenever Arisen Rider attacks, creatures your opponents control get -1/-1 until end of turn.
If Arisen Rider or another creature or planeswalker would die, exile it instead.

Target creature gets +2/+2 and gains indestructible until end of turn.

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
Whenever a creature you control enters, each opponent loses 1 life.
I, II — Create a 1/1 black Actor creature token with lifelink.
III — Each opponent loses life equal to the number of tokens you control. You gain life equal to the life lost this way.