msem-instigator

Create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)
Draw a card.

({T}: Add {B}, {G}, or {U}.)
Verdant Dominion enters tapped.

Whenever Marine Delver attacks, draw a card.

When Croakfolk Troubadour enters, draw a card.

Exile target creature. Return that card to the battlefield under its owner's control at the beginning of the next end step.
Metamorph {2}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up and cast it at any time for its metamorph cost.)

{T}: Add {C}.
{4}, {T}, Sacrifice Eon Campfire: Destroy target artifact or nonbasic land.

{T}: Add {C}.
Shrine of the World-Shepherd's power and toughness are each equal to the number of differently named lands you control.
{3}{G}: Shrine of the World-Shepherd becomes a Beast creature in addition to its other types until end of turn.

(As an Encounter enters, choose an opponent to protect it. You and others can attack it. When defense counters are removed, create a 0/0 Army token if you don't control one, then put that many +1/+1 counters on a Army you control.)
When Dawn Over Kaneh enters, return any number of creature cards from your graveyard with total mana value X or less to the battlefield. They become Armies in addition to their other types.

You may have Blurry Counterpart enter as a copy of any creature on the battlefield.
Mirage {1}{U} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Each player draws a card, then target player mills X cards, where X is the number of cards players have drawn this turn.

Flying
When Kaalia's Abomination enters or dies, it deals 2 damage to target opponent. Then that player discards two cards.

Trample
Rift Prowler enters with X +1/+1 counters on it, where X is your fealty to Forests. (Each Forest you control counts towards your fealty to Forests.)

When Borderland Garrison enters, it deals 1 damage to up to one target creature and 1 damage to you.

Thunderous Applause deals damage to any target equal to the number of tapped creatures you control.

Whenever Adept Lieutenant attacks, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)
{1}, Sacrifice an Idol: Put a +1/+1 counter on Adept Lieutenant.

Whenever a creature dies, put a +1/+1 counter on each creature you control with power less than it.
{3}{G}, Sacrifice a creature: Draw cards equal to the sacrificed creature's power.

Vigilance, reach
As a noncreature spell resolves, exile it instead of putting it anywhere else.

Untap target creature and gain control of it until end of turn. That creature gains haste until end of turn.

When Harvest Blighter enters, create a black Aura Curse enchantment token named Rotting Away attached to target player. The token has enchant player and “Whenever a creature enters under enchanted player's control, if it has toughness 2 or greater, put a -1/-1 counter on that creature.”

Whenever Evaldi's Muse or another nontoken creature you control enters, you gain 2 life.
When Evaldi's Muse leaves the battlefield, create two 1/1 green and blue Elf creature tokens.

Dominance — At the beginning of combat on your turn, if you control the creature with the greatest power or tied for the greatest power, you may pay {R}. If you do, gain control of target creature an opponent controls until end of turn. Untap that creature. It gains haste until end of turn.

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I, II — War's Sorrow deals 1 damage to any target.
III — Each player sacrifices another permanent. Put War's Sorrow on top of its owner's library unless a player has it deal 3 damage to them.

When Fiend of Convenience enters, destroy target creature an opponent controls.
Whenever Fiend of Convenience attacks, each opponent loses 3 life.

Enchant creature
Enchanted creature gets +1/+1.
Sacrifice Bear Necessities: Enchanted creature gains indestructible until end of turn.

{U}, {T}: Sacrifice any number of nontoken creatures. Create an X/X blue Horror creature token, where X is the total power of those creatures. Then if X is 4 or greater, you may transform Performer of Brilliance.