msem-instigator

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.

Menace
Whenever Operative GINGER attacks or you cast a blue or white spell, Operative GINGER deals 1 damage to any target.

Ward {3}
Whenever Operative SPORTY attacks or you cast a blue or black spell, put a +1/+1 counter on Operative SPORTY.

Ophan Titan gets +3/+3 as long as there are no nonland cards in your graveyard.
Morph {1}{G} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

When Ophorio Scavenger enters, 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.”)
Ophorio Scavenger gets +1/+1 as long as you control three or more artifacts.

{T}: Add {G}. If you control an attacking creature, add one mana of any color instead.

Whenever Oracle of Flames becomes tapped, up to one target creature you control gets +2/-2 until end of turn.

Whenever another nonland permanent you control enters, return that permanent to its owner's hand at the beginning of the next end step.

Whenever you sacrifice an Idol, put a +1/+1 counter on Orchard Botanist.

Whenever Ore Tunneler deals damage to an opponent, tap target land they control. It doesn't untap during its controller's next untap step.

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] You may discard a card. If you do, draw a card.
[Lore III] Create a token that's a copy of another target creature you control, except it has haste. Sacrifice it at the beginning of the next end step.

Destroy target artifact or enchantment with mana value 3 or less.
Ferocious — You gain 4 life if you control a creature with power 4 or greater.

Equipped creature gets +1/+1.
Whenever equipped creature deals combat damage to a player, Ornamental Longbow deals 1 damage to any target.
Equip {2}

{1}, Sacrifice Ornate Incense: Draw a card. You gain 1 life.

When Ornery Bull enters, return a creature you control to its owner's hand.

Whenever Orphan Prodigy is dealt damage, it deals that much damage to target player.
Attain {4}{R} ({4}{R}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

Defender
Whenever another creature you control enters, Orphan of the Nav gets +1/+1 until end of turn and can attack as though it didn't have defender this turn.

All creatures able to block Orphaned Nuckalavee do so.

You may cast spells as though they had flash.

{T}, Discard a card: Draw a card.
{2}{R}, {T}: Copy target instant or sorcery spell you control. You may choose new targets for the copy. Activate only if you have four or more instant and/or sorcery cards in your graveyard.

All creatures able to block Osheen Courtier do so.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

({T}: Add {G}.)
Wanderlust — Otherworldly Forest enters tapped unless you control four or more other differently named lands.
{1}, {T}: Add one mana of any color.

Reveal the top four cards of your library. You may put a creature or land card from among them into your hand. Put the rest into your graveyard.

({T}: Add {R}.)
Wanderlust — Otherworldly Mountain enters tapped unless you control four or more other differently named lands.
{1}, {T}: Add one mana of any color.

Manifest the top card of your library and the bottom card of your library. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)