Rootha, Mastering the Moment

At the beginning of combat on your turn, if you've cast an instant or sorcery spell this turn, create an X/X blue and red Elemental creature token with flying and haste, where X is the greatest mana value among instant and sorcery spells you've cast this turn.

Muse Seeker

Opus — Whenever you cast an instant or sorcery spell, draw a card. Then discard a card unless five or more mana was spent to cast that spell.

Seize the Spoils

As an additional cost to cast this spell, discard a card.
Draw two cards and create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Talisman of Creativity

{T}: Add {C}.
{T}: Add {U} or {R}. This artifact deals 1 damage to you.

Scorched Geyser

({T}: Add {U} or {R}.)
This land enters tapped unless you control two or more basic lands.

Molten-Core Maestro

Menace
Opus — Whenever you cast an instant or sorcery spell, put a +1/+1 counter on this creature. If five or more mana was spent to cast that spell, add an amount of {R} equal to this creature's power.

Maestro's Gift

Create a token that's a copy of target creature you control. That token gains haste until end of turn.

Inspired Skypainter

Flying
When this creature enters and whenever one or more creature tokens you control deal combat damage to a player, this creature becomes prepared. (While it's prepared, you may cast a copy of its spell. Doing so unprepares it.)

Inspired Skypainter // Maestro's Gift

Prismari, the Inspiration

Flying
Ward—Pay 5 life.
Instant and sorcery spells you cast have storm. (Whenever you cast an instant or sorcery spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Improvisation Capstone

Exile cards from the top of your library until you exile cards with total mana value 4 or greater. You may cast any number of spells from among them without paying their mana costs.
Paradigm (Then exile this spell. After you first resolve a spell with this name, you may cast a copy of it from exile without paying its mana cost at the beginning of each of your first main phases.)

Leitmotif Composer

Whenever this creature deals combat damage to a player, draw a card.
Whenever you cast an instant or sorcery spell with mana value 5 or greater, create a token that's a copy of this creature.
{2}{U}: Creatures named Leitmotif Composer can't be blocked this turn.

Magma Opus

Magma Opus deals 4 damage divided as you choose among any number of targets. Tap two target permanents. Create a 4/4 blue and red Elemental creature token. Draw two cards.
{U/R}{U/R}, Discard this card: Create a Treasure token.

Crucible of Worlds

Mountain

Dreamscape Artist

{2}{U}, {T}, Discard a card, Sacrifice a land: Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

Wild Idea

Search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.

Sanar, Unfinished Genius

Sanar enters prepared. (While it's prepared, you may cast a copy of its spell. Doing so unprepares it.)
{T}: Create a Treasure token. Activate only if you've cast an instant or sorcery spell this turn.

Sanar, Unfinished Genius // Wild Idea

Colorstorm Stallion

Ward {1}, haste
Opus — Whenever you cast an instant or sorcery spell, this creature gets +1/+1 until end of turn. If five or more mana was spent to cast that spell, create a token that's a copy of this creature.

Resonating Lute

Lands you control have "{T}: Add two mana of any one color. Spend this mana only to cast instant and sorcery spells."
{T}: Draw a card. Activate only if you have seven or more cards in your hand.

Island

Turbulent Springs

({T}: Add {U} or {R}.)
This land enters tapped unless your opponents control eight or more lands.

Stormcarved Coast

This land enters tapped unless you control two or more other lands.
{T}: Add {U} or {R}.

Prismari Pianist

Whenever you cast an instant or sorcery spell, create a 1/1 blue and red Elemental creature token. If that spell's mana value is 5 or greater, create three of those tokens instead.