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.

Search your library for up to six cards and exile them face down. Shuffle, then draw a card.

As an additional cost to cast this spell, you may tap any number of untapped tokens you control. This spell costs {1} less to cast for each token tapped this way.
Whenever Organic Dreadnought enters or attacks, tap target permanent an opponent controls. That permanent doesn't untap during its controller's next untap step.

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.

Whenever Orria Mirrorpelt becomes the target of a spell, exile that spell. If Orria Mirrorpelt was its only target, copy it for each other creature target player controls. Each copy targets a different one of those creatures.

Flash
Oscanthor, Trader's Ruin can't be blocked.
Whenever a creature you control deals combat damage to a player, draw a card.

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 {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.

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.

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

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

Whenever you cast a noncreature spell, up to one target artifact or non-Aura enchantment you control becomes a 3/3 creature in addition to its other types until end of turn.

Exile the top X cards of target opponent's library. You may play those cards for as long as they remain exiled, and you may spend mana as though it were mana of any color to cast them.

Prowess
Foresight — When Outpost Merchant enters, if you've drawn two or more cards this turn, create two 1/1 white Bird creature tokens with flying.

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.”)

Counter target spell if you have more cards in hand than its controller.

Draw three cards, then reveal your hand.

Enchant player
Whenever enchanted player becomes the target of a spell or ability they don't control, if it isn't a copy, its controller copies it.

Counter target spell. For each other card named Overcharge in your graveyard, create a colorless Canister artifact token with “{T}, Sacrifice this artifact: Add {C}.”

Any number of target players each draw seven cards, then discard seven cards.

When Overwhelming Paperwork enters or is put into a graveyard from the battlefield, return up to one target creature to its owner's hand.
{3}{U}{U}: Sacrifice Overwhelming Paperwork. Activate only as a sorcery.

Counter target spell unless its controller pays {X}. You may cast a spell with mana value X or less from your hand without paying its mana cost.

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