Spell Fusion is the ability to infuse Sub-Weapons (Dagger, Axe, Sacred Fist, Holy Water, Holy Book, and Cross) with the power of Magic Books in Castlevania: Harmony of Dissonance to unleash devastating magical attacks similar to the Item Crash ability the Belmonts have in other Castlevania games. There are 5 different books of magic in the game: Fire Book, Ice Book, Bolt Book, Wind Book, and the Summoning Tome (non-elemental).

Spell Fusion List

Dagger: Mirage Knife - Juste starts floating, surrounding himself with 9 daggers which burst into flames, transforming into giant fireballs which launch in every direction and ricochet on the screen multiple times.
Axe: Soul of Hydra - Juste unleashes 2 dragons made out of fire which home in on the nearest enemy.
Sacred Fist: Shining Knuckle - Juste fires 6 balls of fire.
Holy Water: Bounding Flame - Juste creates a fireball thats travel along the ground.
Holy Book: Heat Spiral - A Bible is released and spinnning flames fan out all around it.
Cross: Burning Cross - Juste creates a giant cross which launches a swirling fire blast on impact.

Dagger: Magic Missile - Juste attacks with multiple homing projectiles.
Axe: Hail Stone - Juste creates a giant chunk of ice which falls from the heavens on a target.
Sacred Fist: Icicle Dash - Juste attacks with a powerful knuckle made of ice.
Holy Water: Ice Cubic - Three ice blocks form on a target.
Holy Book: Judgement Water - Juste unleashes blue fire on both sides of him.
Cross: Ice Servant - Juste creates a spinning ice cross which sprays icicles (functions like a familiar). The ice cross will get smaller as it sprays icicles, until it finally disappears.

Dagger: Sparkling Rain - Juste throws several energy blades to the sky which then fall on enemies within range.
Axe: Lightning Bolt - Juste calls upon lightning to attack most enemies on the screen.
Sacred Fist: Homing Thunder - Launches concentrated thunderbolts at the enemy.
Holy Water: Ground Bolt - Lightning moves around the screen, damaging everything in its path.
Holy Book: Shield - Two balls of energy float in front of Juste, damaging anything that touches them.
Cross: Holy Cross - Juste is engulfed in light from the heavens and floats in the sky, unleashing giant crosses which spiral around him.

Dagger: Thousand Dagger - Juste throws a stream of daggers.
Axe: Axe Trap - An axe swirls around Juste (based on the classic item crash).
Sacred Fist: Fighting Spirit Fist - Juste fires a powerful energy ball from his fists, similar to the Hadōken from the Street Fighter series.
Holy Water: Hydro Typhoon - Holy water rains from the heavens.
Holy Book: Protect Bible - Juste surrounds himself with several Bibles that act as a shield.
Cross: Guardian Cross - Juste surrounds himself with crosses that act as a protective barrier.

Dagger: Summon Garuda - The giant bird Garuda is summoned to attack with a rain of sharp feathers.
Axe: Evil Wing - A winged devil is summoned, which turns its wings into axes that fly around the screen.
Sacred Fist: Summon Asura - Juste summons Asura, who unleashes a flurry of punches everywhere.
Holy Water: Summon Aquarius - Juste summons an angel which flies around showering everything in holy water.
Holy Book: Summon Fairie - A fairie is summoned to attack the closest enemy with a hammer.
Cross: Summon Warlock - A mysterious sorcerer with a cane and glowing red eyes is summoned, calling upon meteors from the heavens.
No Sub-Weapon: God Bless - Restores Juste's health.

Trivia