msem-instigator

Create three 1/1 green Saproling creature tokens.

When Byron, Unlikely Hero enters, put a +1/+1 counter on each other Citizen or Peasant you control.
Whenever a nontoken creature you control with a +1/+1 counter on it dies, create a 1/1 white Peasant creature token.

Codex — Eleventh Hour Breakthrough; Mentorb; Ostracizer Orb; Possibility Engine; Sealed Riftway; Self Replication. (As this enters, conjure its contents into a shuffled face-up additional library.)
{T}, Sacrifice an artifact: Draw a card from the codex's library.

At the beginning of combat on your turn, target creature gets +1/+1 and gains haste until end of turn.

Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on Oracle of Tides.

Gloam Gullet gets +1/+1 and has menace as long as you own a land card in exile or in your graveyard.

Double strike
Whenever Eldan Jackson deals combat damage, return target permanent card with mana value 3 or less from your graveyard to the battlefield.

At the beginning of your upkeep, put a crop counter on Homestead.
{G/W}, Remove a crop counter from Homestead: Put a +1/+1 counter on target creature.
{G/W}, Remove three crop counters from Homestead: Put a +1/+1 counter on each creature you control.

({T}: Add {R}.)
Rousing Rubble enters tapped.
Double strike
{2}{R}{R}: Rousing Rubble becomes a creature in addition to its other types until end of turn.

Flash
When Ambush Gharial enters, it fights up to one target creature. If that creature would die this turn, exile it instead.

As an additional cost to cast this spell, sacrifice a permanent.
Draw two cards.

Whenever Savvy Saboteur attacks, target creature defending player controls can't block target creature you control this turn.

Breach (Whenever this deals combat damage to a player, you may have it become an Aura Curse until your next turn. Attach it to that player.)
Recursive — As long as Mayar, Nullcrowned is a Curse, they have all nonrecursive abilities of other Curses and creatures with breach you control.
Pay 3 life: Target enchantment creature gains haste and menace until end of turn.

Cliffside Entrance enters tapped unless you have 15 or less life.
{T}: Add {R} or {W}.

When Embrace the Veil enters, you may exile target nonland permanent you don't control until Embrace the Veil leaves the battlefield.
Whenever you cast a spell with mana value 5 or greater, you may put a card exiled with Embrace the Veil into its owner's graveyard and return Embrace the Veil to its owner's hand.

Stampede — Whenever Etlan High Priest and a creature with greater power attack, Etlan High Priest gets +1/+1 until end of turn. Then you gain 1 life and scry 1.

{T}: Add {C}.
{T}, Exile two cards from your graveyard: Add {W} or {U}.

Target player draws two cards and loses 2 life.

Trample
Primitive Berserker's power is equal to the number of Goblins you control.

Whenever Encouraging Bulwark attacks, you may put a +1/+1 counter on each creature you control that's enchanted and/or has one or more counters on it.

Lifelink
At the beginning of your end step, if you gained life this turn, put a +1/+1 counter on Backstage Manager.

Harmony — Pyrodancer deals 1 damage to each opponent.
When Pyrodancer enters, harmonize. (Trigger up to one harmony of one permanent you control.)

Trample, haste
Herald of Untold Riches gets +1/+1 for each color among other spells you've cast this turn.

Enchant creature
When Ravage of Moments enters and at the beginning of your upkeep, put a -1/-1 counter on enchanted creature.

Deception {U}{B} ({U}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Oshiruko Conspirator deals combat damage to a player, you may discard a Rogue card. If you do, search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.