msem-instigator

When Oracle Crab enters, scry 2. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

When Oracle of Edicts enters, adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)
Whenever an Aura you control enters, scry 1.

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

Target creature gets -5/-5 until end of turn.
Judge up to one target creature you control. (Honor it by putting a +1/+1 counter on it or condemn it by sacrificing it to draw a card.)

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

Oreskos Warden has lifelink as long as you control an enchantment.

Whenever Organ Scavenger perseveres, each opponent loses 2 life. (A creature perseveres when it survives damage.)

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.

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

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

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.

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.)

Lifelink
At the beginning of your upkeep, Osgaerith Desecrator deals 1 damage to up to one target creature.

Deception {B} ({B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
When Oshiruko Operative enters, target player loses 1 life.

Deception {2}{U} ({2}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
When Oshiruko Silencer enters, return target creature to its owner's hand.

Distorted (This creature can be blocked by tapped creatures but not untapped creatures.)

When Osseous Augur enters, target creature an opponent controls gets -1/-1 until end of turn. If that creature's controller is cursed, that creature gets -3/-3 until end of turn instead.

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.

Enchant player
At the beginning of enchanted player's upkeep, they tap an untapped creature they control.

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.)

{1}{W}, Exile Outcast of the Folded Fan from your graveyard: Create a 1/1 white Bird creature token with flying. Activate only as a sorcery.

Outer Wall Guard enters with a +1/+1 counter on it if you gained life this turn.