Overblaze

Each time target permanent would deal damage to a permanent or player this turn, it deals double that damage to that permanent or player instead.
Splice onto Arcane {2}{R}{R} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Desperate Ritual

Add {R}{R}{R}.
Splice onto Arcane {1}{R} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Veil of Secrecy

Target creature gains shroud until end of turn and can't be blocked this turn. (A creature with shroud can't be the target of spells or abilities.)
Splice onto Arcane—Return a blue creature you control to its owner's hand. (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Soratami Savant

Flying
{3}, Return a land you control to its owner's hand: Counter target spell unless its controller pays {3}.

Through the Breach

You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice that creature at the beginning of the next end step.
Splice onto Arcane {2}{R}{R} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Inalla, Archmage Ritualist

Eminence — Whenever another nontoken Wizard you control enters, if Inalla, Archmage Ritualist is in the command zone or on the battlefield, you may pay {1}. If you do, create a token that's a copy of that Wizard. The token gains haste. Exile it at the beginning of the next end step.
Tap five untapped Wizards you control: Target player loses 7 life.

Dualcaster Mage

Flash
When Dualcaster Mage enters, copy target instant or sorcery spell. You may choose new targets for the copy.

Uyo, Silent Prophet

Flying
{2}, Return two lands you control to their owner's hand: Copy target instant or sorcery spell. You may choose new targets for the copy.

Eerie Procession

Search your library for an Arcane card, reveal that card, put it into your hand, then shuffle.

Snapcaster Mage

Flash
When Snapcaster Mage enters, target instant or sorcery card in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost. (You may cast that card from your graveyard for its flashback cost. Then exile it.)

Horobi's Whisper

If you control a Swamp, destroy target nonblack creature.
Splice onto Arcane—Exile four cards from your graveyard. (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Goryo's Vengeance

Return target legendary creature card from your graveyard to the battlefield. That creature gains haste. Exile it at the beginning of the next end step.
Splice onto Arcane {2}{B} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Hisoka, Minamo Sensei

{2}{U}, Discard a card: Counter target spell if it has the same mana value as the discarded card.

Azami, Lady of Scrolls

Tap an untapped Wizard you control: Draw a card.

Soratami Seer

Flying
{4}, Return two lands you control to their owner's hand: Discard all the cards in your hand, then draw that many cards.

Glacial Ray

Glacial Ray deals 2 damage to any target.
Splice onto Arcane {1}{R} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Evermind

(Nonexistent mana costs can't be paid.)
Draw a card.
Splice onto Arcane {1}{U} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Mirror Gallery

Soulless Revival

Return target creature card from your graveyard to your hand.
Splice onto Arcane {1}{B} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Hideous Laughter

All creatures get -2/-2 until end of turn.
Splice onto Arcane {3}{B}{B} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Tomoya the Revealer

{3}{U}{U}, {T}: Target player draws X cards, where X is the number of cards in your hand.

Jushi Apprentice

{2}{U}, {T}: Draw a card. If you have nine or more cards in hand, flip Jushi Apprentice.

Jushi Apprentice // Tomoya the Revealer

Soulblast

As an additional cost to cast this spell, sacrifice all creatures you control.
Soulblast deals damage to any target equal to the total power of the sacrificed creatures.

Reweave

Target permanent's controller sacrifices it. If the player does, they reveal cards from the top of their library until they reveal a permanent card that shares a card type with the sacrificed permanent, put that card onto the battlefield, then shuffle.
Splice onto Arcane {2}{U}{U} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Psychic Puppetry

You may tap or untap target permanent.
Splice onto Arcane {U} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)