High Fae Trickster

Flash (You may cast this spell any time you could cast an instant.)
Flying
You may cast spells as though they had flash.

Shimmer Myr

Flash
You may cast artifact spells as though they had flash.

Cunning Nightbonder

Flash
Spells with flash you cast cost {1} less to cast and can't be countered.

Tidal Barracuda

Any player may cast spells as though they had flash.
Your opponents can't cast spells during your turn.

Valley Floodcaller

Flash
You may cast noncreature spells as though they had flash.
Whenever you cast a noncreature spell, Birds, Frogs, Otters, and Rats you control get +1/+1 until end of turn. Untap them.

Borne Upon a Wind

You may cast spells this turn as though they had flash.
Draw a card.

Fire Lord Azula

Firebending 2 (Whenever this creature attacks, add {R}{R}. This mana lasts until end of combat.)
Whenever you cast a spell while Fire Lord Azula is attacking, copy that spell. You may choose new targets for the copy. (A copy of a permanent spell becomes a token.)

Leyline of Anticipation

If this card is in your opening hand, you may begin the game with it on the battlefield.
You may cast spells as though they had flash.

Renari, Merchant of Marvels

You may cast Dragon spells and artifact spells as though they had flash.
Choose a Background (You can have a Background as a second commander.)

Mai and Zuko

Firebending 3
You may cast Ally spells and artifact spells as though they had flash.

Vedalken Orrery

You may cast spells as though they had flash.

Rootwater Shaman

You may cast Aura spells with enchant creature as though they had flash.

Sigarda's Aid

You may cast Aura and Equipment spells as though they had flash.
Whenever an Equipment you control enters, you may attach it to target creature you control.

Azula, Cunning Usurper

Firebending 2 (Whenever this creature attacks, add {R}{R}. This mana lasts until end of combat.)
When Azula enters, target opponent exiles a nontoken creature they control, then they exile a nonland card from their graveyard.
During your turn, you may cast cards exiled with Azula and you may cast them as though they had flash. Mana of any type can be spent to cast those spells.