msem-instigator

When Njel Crocodile enters, you may have it fight target creature. (Each deals damage equal to its power to the other.)

When Seductive Seashell enters, target player mills two cards.
{2}, Sacrifice Seductive Seashell: Target player mills four cards.

Target attacking creature gets +3/+1 until end of turn.
Conjure a card named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

Whenever you cycle a card, scry 1. (Do this before you draw.)
{W}{U}{B}{R}{G}, Sacrifice Maelstromancy: Return up to three target cards with cycling abilities from your graveyard to your hand.

Vigilance, lifelink

Snowy Misthorn can block creatures with distorted as though it was tapped.

Destroy four target creatures.

Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)
When Aith Aera Sentinel enters, create a 1/1 green Elf creature token.

When you cast this spell, copy it for each player that has 8 or less life. (The copies have the same target.)
Traitor's Execution deals 3 damage to target player.

({T}: Add {R} or {G}.)
Autumn Canopy enters tapped.
{1}, {T}: Add {R}{R} or {G}{G}.

First strike
Noncreature spells cost {1} more to cast as long as their controller is horrific. (A player is horrific as long as they've sacrificed a permanent or discarded a card this turn.)

Flash
{U}, Sacrifice Seal of Approval: Counter target spell unless its controller pays {2}.

Flash

When Blackwall Ramparts enters, exile up to two target nonland permanents you don't control with total mana value 8 or less until Blackwall Ramparts leaves the battlefield.
Whenever you draw a card, you gain 1 life.

Trial 4 (As you cast this spell, an opponent of your choice may pay 4 life. If they don't, they fail the trial.)
Search your library for an Angel card, reveal it, put it into your hand, then shuffle. If the trial was failed, non-Angel, non-God creatures can't attack or block until your next turn.

When Lone Stranger enters, if you control no other creatures, create two 1/1 colorless Spirit creature tokens.

Double strike, vigilance
At the beginning of combat on your turn, create X 1/1 red Dwarf creature tokens with haste, where X is the number of embattled nontoken creatures you control. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

(As this Discovery enters and after your draw step, add a progress counter. Stop after you've discovered.)
Archive 6 (As this enters, shuffle the top six cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
Draw a card from each of your libraries.
discover — When you draw the last card from the archived library, create a 4/4 blue Sphinx Wizard creature token with flying.

({T}: Add {B} or {G}.)
Whenever Nomad's Township becomes tapped, you lose 1 life unless you control two or more basic lands.

Destroy target artifact or land.
Kindle 2—{R}, Sacrifice an artifact or land. ({R}, Sacrifice an artifact or land, Exile this card from your graveyard: Create two 1/1 colorless Elemental creature tokens. Kindle only as a sorcery.)

Counter target instant or Aura spell that targets a permanent you control.

{T}, Sacrifice Evolving Wilds: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Whenever you discard a card, choose up to one that hasn't been chosen this turn —
• Draw a card.
• Tap target creature. Put a stun counter on it.
• Create a 2/2 blue Jellyfish enchantment creature token with flying.

Auditioning for a color causes you to create a 1/1 colorless Construct Actor creature token, then create one of the audition's Role tokens.

Menace
Foresight — Whenever you draw your second card each turn, put a +1/+1 counter on Telani Scammer.