Flash
Enchant creature
Enchanted creature gets -2/-0 and loses all abilities. (Mutating onto the creature won't give it new abilities. It can gain abilities in other ways.)

You may cast this spell as though it had flash. If you cast it any time a sorcery couldn't have been cast, the controller of the permanent it becomes sacrifices it at the beginning of the next cleanup step.
Enchant creature
Enchanted creature has shroud.

This spell costs less to cast if it targets a blue spell.
Counter target spell unless its controller pays .

Search your library for an instant card or a card with flash, reveal it, put it into your hand, then shuffle.
Flashback

Search your library for an instant or sorcery card, reveal it, then shuffle and put that card on top.

Create a token that's a copy of target permanent. If was spent to cast this spell, instead create a token that's a copy of that permanent, except the token has "When this token enters, if it's a creature, it fights up to one target creature you don't control."

If a Wizard you control entering causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Whenever you draw a card, you may pay . If you do, put a +1/+1 counter on this creature and create a 1/1 blue Tentacle creature token.

You may have this creature enter as a copy of any creature on the battlefield.
Renew — , Exile this card from your graveyard: Put a +1/+1 counter on target nonlegendary creature you control. Each other creature you control becomes a copy of that creature until end of turn. Activate only as a sorcery.

When this creature enters, surveil 3.

Look at the top two cards of your library. Put one of them into your hand and the other into your graveyard.
Madness

During turns other than yours, spells you cast cost less to cast.

Flying
Each other Merfolk you control with a +1/+1 counter on it has flying.
At the beginning of combat on your turn, target creature you control connives.

Flying
Power-up — : Put a +1/+1 counter on Namora. Create two 1/1 blue Merfolk creature tokens.

Whenever this creature becomes tapped, untap another target permanent. This ability triggers only once each turn.

Choose target creature you control. Each other creature becomes a copy of that creature until end of turn, except it isn't legendary.

Enchant creature
At the beginning of each upkeep, if enchanted creature is untapped, tap it.

Flying
When this card is put into your graveyard from your library, you may put it onto the battlefield.

: Add for each counter on Nardole. Spend this mana only to cast noncreature spells.
Undying
Doctor's companion (You can have two commanders if the other is the Doctor.)

Copy target instant or sorcery spell, then return it to its owner's hand. You may choose new targets for the copy.

Flash
When Naru Meha enters, copy target instant or sorcery spell you control. You may choose new targets for the copy.
Other Wizards you control get +1/+1.

First strike, protection from red

Whenever this creature attacks or blocks, target opponent reveals cards from the top of their library until they reveal a creature card. This creature becomes a copy of that card until end of turn. Then that player puts all cards revealed this way on the bottom of their library in a random order.

Raid — At the beginning of your end step, if you attacked this turn, target opponent mills four cards.

Flash
Flying
Whenever this creature or another Spirit you control enters, tap target creature an opponent controls.

Flash
Flying
When this creature enters, up to one target creature an opponent controls gets -2/-0 until end of turn.

Whenever a nontoken Zombie you control enters, create a token that's a copy of that creature.

Whenever Neerdiv becomes tapped, target player mills cards equal to its power.
Whenever you cast a spell from your graveyard or activate an ability of a card in your graveyard, draw a card and put a +1/+1 counter on Neerdiv.