msem-instigator

Target player mills seven cards.
Inscribe {3}{U}{B} ({3}{U}{B}: Exile this card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

Onoran Runeglyphs enters tapped.
{T}: Add two mana in any combination of colors from among creatures you control.
Menagerie — {2}, {T}: Draw a card. Activate only if there are five or more creature types among creatures you control.

Flying
Creatures you don't control have “{T}: This creature fights Ontarachie Apex. Activate only as a sorcery.”

Germinate, then creatures you control that are Saprolings or have counters on them gain indestructible until end of turn. (To germinate, put a +1/+1 counter on a creature or create a 1/1 green Saproling creature token.)

Whenever you draw a card, put a +1/+1 counter on Ontarachie Curio.
{T}, Remove a +1/+1 counter from Ontarachie Curio: Create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”
{1}{G}: Ontarachie Curio becomes a green 2/1 Dryad creature until end of turn. (It's no longer an artifact.)

Whenever you draw a card, put a +1/+1 counter on Ontarachie Dryad.
Remove a counter from Ontarachie Dryad: Create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”

When Ontarachie Emissary leaves the battlefield, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

When Ontarachie Envoy enters, nourish, then germinate. (To nourish, put a +1/+1 counter on this creature or create a 1/1 white Citizen creature token. To germinate, put a +1/+1 counter on a creature you control or create a 1/1 green Saproling creature token.)

Vigilance (Attacking doesn't cause this creature to tap.)
Sacrifice a Fungus, Saproling, Plant, or Insect: Put a +1/+1 counter on Ontarachie Forager.

Whenever Ontarachie Hunter attacks, each opponent loses 1 life.
At the beginning of your end step, if an opponent has 10 or less life, transform Ontarachie Hunter.

When Onward to War enters, draw a card, then choose a card name.
Whenever one or more creatures you control with the chosen name attack, look at the top four cards of your library. Put a creature or enchantment card with mana value 3 or less from among them into your hand. Put the rest on the bottom of your library in any order.

When Onya the Gilded dies, search your library for a planeswalker card with a different name, reveal it, put it into your hand, then shuffle.
[–1]: Draw up to two cards. For each of those cards, pay 1 life or discard a card.
[–2]: Creatures you control get +1/+1 until your next turn.
[–3]: Onya the Gilded deals 3 damage to any target and you gain 3 life.

Lifelink
Whenever a planeswalker dies, Onya's Chosen deals 3 damage to target creature or player.

Deathtouch
Whenever Oozing Adder attacks, you may have target creature defending player controls block it this combat if able.

Opalescent Heirloom enters with a charge counter on it for each color of mana spent to cast it.
Equipped creature gets +1/+1 for each charge counter on Opalescent Heirloom.
Equip—{3} or remove a charge counter from Opalescent Heirloom.

{T}: Add {U} or {R}. You lose 1 life unless you have less life than an opponent.

Flying
At the beginning of your end step, up to one other target creature you control voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)
Whenever a creature you control phases in, you may have it become a copy of target creature you control until end of turn.

Search your library for a land card, reveal it, then shuffle and put that card on top. (Then exile this card. You may play the land later from exile.)

At the beginning of your upkeep, each player conjures a card named Data-Point into their hand. (It's a sorcery that costs {2} with “Draw a card.”)

Return target creature card from your graveyard to the battlefield, then rediscover a creature card. (Look at the top card of your library. You may reveal it and put it into your hand if it's a creature card. Otherwise, put it back or into your graveyard.)

For each nonland token you control, create a token that's a copy of it.

Destroy target artifact. Scry 1.

At the beginning of your upkeep, reveal the bottom card of your library. You may cast it if it's a creature card. Otherwise, exile it.

Trample
Whenever Openmaw Demon or another Azra or Demon you control enters, you may exile target card from a graveyard.

Opera House enters tapped.
When Opera House enters, add one mana of any color.
{T}, Sacrifice Opera House: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.