msem-instigator

Flash (You may cast this spell any time you could cast an instant.)
Flying
When Orichi of the Cold Mist enters, exile another target creature you control. Return that card to the battlefield under its owner's control at the beginning of the next end step.

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.

Flying
Whenever an opponent casts a spell, counter it unless that player pays {1} for each spell cast before it this turn.

Flash
Flying
When Oshin enters, counter target spell if its mana value is less than or equal to the number of spells you've cast this turn.

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.

When Oshiruko Purifier enters, create a 2/2 colorless Spirit creature token.
Colorless creatures you control have lifelink.

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.

{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.

{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.

Vigilance, lifelink

Lifelink
Outskirts Provider enters with a +1/+1 counter on it if a creature attacked this turn and wasn't blocked.

Hexproof
When Overburdened Trader enters, create three 1/1 colorless Construct artifact creature tokens.

When Overconfident Batter dies, if it's enchanted or you cast a spell that targeted it this turn, you gain 3 life.

Overgrown Siren must be blocked if able.

Trample
Overgrown Spellroot gets +1/+1 for each creature token you control.
When Overgrown Spellroot enters, create four 1/1 black Worm creature tokens.

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.

Flash
Flying
Whenever you cast another spell with flash or an instant, conjure a card named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

{T}: Target player loses 1 life.
Whenever you cast a spell from your graveyard, untap Paincaller.

{1}, Discard a card: Painted Watcher gets +1/+1 and becomes the color of your choice until end of turn.

Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)
When Painwield Explorer dies, it deals damage equal to its power to target player or planeswalker.

Whenever a creature dies, Pakka, the Shadowcloak deals 1 damage to each opponent.

Encourage ({T}: Another target creature you control gets +1/+1 until end of turn. Encourage only as a sorcery.)
Whenever Paladin's Attendant encourages a creature, that creature gains first strike until end of turn.