msem-instigator

Whenever a creature you control attacks and isn't blocked, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on that creature, then put the card back or put it into your graveyard.)

Equipped creature gets +1/+1.
Whenever equipped creature attacks, tap up to one target creature.
Equip {1}

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Whenever you cast a spell during an opponent's turn, tap target nonland permanent.

Whenever you cast a spell, you may pay {1}. If you do, Wizened Tortle explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)

Death knell — Each opponent loses 1 life. You gain life equal to the amount of life lost this way. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)
Whenever a creature dies, trigger a death knell of a permanent you control.

Enchant player
At the beginning of enchanted player's upkeep, if they control two or more creatures and/or planeswalkers, they sacrifice a creature or planeswalker.

As an additional cost to cast this spell, sacrifice a creature or planeswalker.
Destroy target creature or planeswalker.

Enchant player
Whenever one or more creatures you control die, enchanted player loses 1 life and you gain 1 life.

When Doomed Widow dies, create a 1/1 white Spirit creature token with flying.

Target creature gets -3/-3 until end of turn. You gain 3 life. (Then exile this card. You may cast the creature later from exile.)

Death knell — All creatures get -1/-1 until end of turn. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)
{B}, Sacrifice a creature: Choose a card in your graveyard with mana value less than the sacrificed creature's mana value. You may cast it without paying its mana cost.

Until end of turn, target creature you control gains “When this creature dies, return it to the battlefield under your control with a +1/+1 counter on it.”

Enchant player
At the beginning of enchanted player's end step, if they cast a spell this turn, they lose 1 life.

Each opponent sacrifices a creature. Whenever one or more players lose life this turn, repeat that process.

Menace
Death knell — Put a +1/+1 counter on Guiltless Wraith. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)

Choose three. You may choose the same mode more than once.
• You draw a card and you lose 1 life.
• Target opponent discards a card and loses 1 life.

Death knell — Return an Aura card with mana value 5 or less from your graveyard to the battlefield. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)
As long as Inconspicuous Otter is enchanted or equipped, he's a 3/4 legendary Otter Rogue named Agent O and has menace.

Remove all counters from target permanent with counters. If it's a creature or enchantment, destroy it.

Enchant player
At the beginning of enchanted player's end step, they lose 2 life unless they discard a card.

Enchant player
At the beginning of enchanted player's end step, gain control of a permanent they control.

When Ominous Presence enters, search your library for a Curse card, reveal it, then shuffle. If it has mana value 4 or less, you may put it onto the battlefield. Otherwise, put it into your hand.
Ominous Presence gets +1/+1 for each Curse attached to your opponents.

Codex — Ser Wayver, the Broken Hour; Suzume Oshiruko; Aguri, Shadow of Doubt; Sukhar, Consort to the Dark; Chi Lee of the Underworld. (As this enters, conjure its contents into a shuffled face-up additional library.)
You may spend mana as though it were mana of any color to cast this codex's contents.

Advance {1}{B} (Cast this for {1}{B} to advance it as it enters. {1}{B}: Advance this as a sorcery.)
Whenever Scarcrawler advances, you lose life equal to its power, then put a +1/+1 counter on it.

Target player discards a card. If they didn't discard an artifact card, you gain 3 life.