msem-instigator

Target player discards a card and gets a poison counter.
Coalesce {4}{B}{B} (You may cast this from your graveyard for {4}{B}{B}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

{T}, Sacrifice a creature: Target player discards a card and loses 1 life. Activate only as a sorcery.

Haste
Caulte Axeslinger gets +2/+2 as long as any opponent lost exactly 3 life this turn.

Reprise {3}{R} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)
Hatsuo's Maneuver deals 1 damage to any target. Create a number of 1/1 red Warrior creature tokens equal to the damage dealt by this spell.

Other creatures you control get +1/+1 as long as you control four or more lands.
{G}, Sacrifice Daisy, the Heart of Chasmek: Creatures you control with base power 1 or less gain indestructible until end of turn.

Each player searches their library for a basic land card, puts it onto the battlefield tapped, then shuffles.

When Sealed Riftway enters, exile up to one target card from a graveyard.
{2}, {T}, Sacrifice Sealed Riftway: Exile target player's graveyard. Draw a card.

Haste
When Volatile Stonework enters, choose target creature or planeswalker an opponent controls.
When Volatile Stonework dies, it deals 4 damage to the chosen creature or planeswalker.

Return target creature card with mana value 3 or less from your graveyard to the battlefield. Put a +1/+1 counter on it. It gains indestructible until end of turn.

When Undead Banneret enters, if you control a legendary creature, each opponent loses 4 life.

Target creature gets +2/+1 and gains trample until end of turn. Create a tapped Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Lifelink
Instant and sorcery spells you control have lifelink.
{2}{R}{W}: Copy target instant or sorcery spell. You may choose new targets for the copy.

Foretell {B}{R} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)
Haste
Whenever Sofia deals combat damage to an opponent, exile the top card of that player's library face down and look at it. You may play that card for as long as it remains exiled, and you may spend mana as though it were mana of any type to cast that spell. Then foretell Sofia. It costs {0} to foretell this way.

Flying
When Tyrant of Tributes enters, target opponent sacrifices X permanents, where X is half the number of permanents they control, rounded up. You gain X life.

Concord — This spell costs {4} less to cast if there are four or more card types among permanents you control.
Vigilance, trample, lifelink, haste

Archive 5 (As this enters, shuffle the top five cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
Whenever a permanent card is put into your graveyard from the battlefield, you may put that card on the bottom of the archived library.

Whenever High-Priestess Nebti attacks or blocks, create a 2/2 white Cat creature token.
{1}{R}{R}, Tap an untapped Cat creature you control: That creature fights target creature you don't control.

Enchant nonland permanent
Enchanted permanent's activated abilities can't be activated and triggered abilities of enchanted permanent don't trigger.

Codex — Unraveling; Unraveling; Unrelenting; Unrelenting; Mindrip; Swipe Secrets. (As this enters, conjure its contents into a shuffled face-up additional library.)
Flash
When Mei's Collection enters, draw a card from its codex.

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.