msem-instigator

Target player mills X cards, where X is the number of cards in your graveyard.
Flashback {3}{U/B}{U/B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Tap up to two target creatures.
Flashback {3}{W/U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Ancient Cairns enters the battlefield tapped.
As Ancient Cairns enters the battlefield, choose a color other than red.
{T}: Add {R} or one mana of the chosen color.

Puzzlebox (Begin the game with this and another card you own from outside the game in the command zone, locked. That card is face down until you unlock this.)
{6}: Unlock Ancient Maze. If the revealed card is green, put it into your hand. Otherwise, put it on top of your library.

When Ancient of the Glade enters the battlefield, put a +1/+1 counter on each other creature you control.
{2}, Remove a +1/+1 counter from a creature you control: That creature gains indestructible until end of turn.

Counter target spell if it shares a color with mana spent to cast Antimagic.

Vigilance
If another creature would die, exile it instead.
At the beginning of your upkeep, return each creature card exiled with Arbiter of Endless Summer to the battlefield under its owner's control.

Whenever Arcane Duelist becomes tapped, target instant or sorcery card with mana value 1 in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost. (You may cast that card from your graveyard for its flashback cost. Then exile it.)

Lifelink
Arcblade Enforcers gets +1/+1 as long as you control an enchantment.

When Archivist Heretic enters the battlefield, you lose 1 life, then investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Target opponent chooses a number. When they do, choose one —
• That player discards their hand, then draws cards equal to the chosen number.
• Archivist's Torment deals damage to that player equal to the chosen number.

Whenever Ashen Host becomes the target of a spell, Ashen Host deals 2 damage to any target.

Enchant creature
When Aura of Leadership enters the battlefield, create four 1/1 white Human Soldier creature tokens.
Enchanted creature gets +2/+2.

This spell costs {2} less to cast if a creature died under your control this turn.
Flying

Create a 5/3 black Horror creature token.
Flashback {1}{B}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

When Barricade Patrol enters the battlefield, create a 1/1 white Human Soldier creature token.
Whenever another creature you control dies, Barricade Patrol deals 1 damage to target player.

Whenever Barricade Watch is dealt damage, put a +1/+1 counter on it. (It must survive the damage to get the counter.)

As an additional cost to cast this spell, remove X +1/+1 counters from among creatures you control.
Create X 2/2 green Wolf creature tokens.

Sacrifice a creature: Put a +1/+1 counter on Blightroot.
Sacrifice a land: Blightroot gains indestructible until end of turn.

At the beginning of each end step, if an opponent lost life this turn, you may put a +1/+1 counter on target creature.
Sacrifice a creature, Sacrifice Blood Cult Covenant: Blood Cult Covenant deals damage equal to the sacrificed creature's power to any target.

Bloodcrazed Acolyte enters the battlefield with a +1/+1 counter on it for each player who lost life this turn.

Creatures you control that have been dealt damage this turn get +2/+0.
When Bloodspawn enters the battlefield, it deals 1 damage to target creature you control.

When Blossom-Ash Trance enters the battlefield, you gain 3 life.
At the beginning of each end step, if you gained 3 or more life this turn, draw a card.

When Blossom-Sower Witch enters the battlefield, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
Whenever you sacrifice a permanent, you gain 1 life.

Haste
At the beginning of your end step, sacrifice Breach Runner unless you return another creature you control to its owner's hand.