msem-instigator

Whenever you cast your first instant or sorcery spell each turn, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Whenever you cast a noncreature spell, creatures you control get +1/+1 until end of turn.

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

Ward—Pay 2 life.
When Orchid Suit enters, target opponent reveals their hand, then exiles a nonland card of their choice from it until Orchid Suit leaves the battlefield.

Identity — When Order's Anointer enters, if you control at least two other creatures that share a creature type with it, creatures you control get +1/+1 until end of turn.

Whenever you cast a black spell, choose up to X, where X is the number of black mana symbols in that spell's mana cost —
• Target player loses 1 life and you gain 1 life.
• Put a -1/-1 counter on target creature.
• You draw a card and you lose 3 life.
• Exile target card in a graveyard.

Your opponents play with the top card of their library revealed.
Your opponents can't cast spells during your turn.
You may play lands and cast spells from the top of an opponent's library during your turn.

Flying, deathtouch
Once each turn, when you cast a spell from your graveyard, you may cast target card in your graveyard with lesser mana value than that spell without paying its mana cost. If that spell would be put into your graveyard, exile it instead.

{2}{W}: Ornate Legionnaire gains first strike until end of turn.

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.

Vigilance
You may look at the top card of your library any time.
Whenever you cast a creature spell from your hand, you may cast the top card of your library without paying its mana cost if it's a creature card with lesser mana value.

Whenever you make first contact, Oscuran Wingmate gains flying until end of turn. (You make first contact the first time each turn you cast a spell with a name not in your graveyard or control already.)

{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.

Oshiruko Whisperwalker can't be blocked except by Rogues.
Whenever a creature is returned to its owner's hand, you may draw a card. If you do, discard a card.

Trample
Whenever Oshu deals combat damage to a player, gain control of target land that player controls. It becomes a 4/4 Elemental creature that's still a land.
As long as you control eight or more lands, Oshu and land creatures you control get +2/+2.

{T}: Add one mana of any color. Spend this mana only to cast a creature spell or activate an ability of a creature.
{5}{W}{U}{B}{R}{G}, Sacrifice Osk, the Maker's Pet: Create Osk Awakened, a legendary 20/20 green Squirrel God creature token with hexproof, trample, and indestructible.

Distorted (This creature can be blocked by tapped creatures but not untapped creatures.)
Oslyd Heretic gets +1/+1 as long as you control no other creatures.

{8}: Create eight 1/1 blue Tentacle creature tokens.
{8}: Counter target spell unless its controller pays {8}.
{8}: Draw eight cards.

Out-of-Depth Amateur can't attack or block alone.
Attain {4}{R} ({4}{R}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

Vigilance, lifelink

Prowess
Whenever Outsider Alchemist deals combat damage to a player, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)

Overgrown Siren must be blocked if able.

When Overgrowth Guardian enters, germinate. (Put a +1/+1 counter on a creature or create a 1/1 green Saproling creature token.)

Flying
When Owl of the Seven Stars enters, scry 2.