Boss Music

Boss Music is used numerous times in the Kingdom Hearts series to indicate that the current battle is with a boss. Most Boss Music is fast-paced and sends a theme of evil or tension. Usually the same song would be used in different boss battles to show the connection between them, e.g. "Shrouding Dark Cloud" is mostly associated with Heartless Bosses and "Squirming Evil" is used commonly for Disney Bosses in Kingdom Hearts.

Awakening

 * Darkside - Dive into the Heart -Destati-

Destiny Islands

 * Darkside - Destiny's Force

Traverse Town

 * Leon - Night of Fate
 * Guard Armor - Shrouding Dark Cloud
 * Opposite Armor - Destiny's Force

Wonderland

 * Queen of Hearts, Card Soldiers and Crank Tower - To Our Surprise
 * Trickmaster - Shrouding Dark Cloud

Olympus Coliseum

 * Cloud (Story) - Shrouding Dark Cloud
 * Cerberus (Story) - Squirming Evil
 * Hades - Squirming Evil
 * Rock Titan - The Deep End
 * Ice Titan - The Deep End
 * Sephiroth - One-Winged Angel (From Final Fantasy VII)

Deep Jungle

 * Sabor - Having a Wild Time
 * Clayton - Having a Wild Time
 * Clayton with Stealth Sneak - Squirming Evil

Agrabah

 * Pot Centipede - Shrouding Dark Cloud
 * Cave of Wonders Guardian - Arabian Dream
 * Jafar - Squirming Evil
 * Jafar (Genie) - Destiny's Force
 * Kurt Zisa - The Deep End

Monstro

 * Parasite Cage (1st Battle) - Shrouding Dark Cloud
 * Parasite Cage (2nd Battle) - Destiny's Force

Atlantica

 * Ursula - Squirming Evil
 * Giant Ursula - The Deep End

Halloween Town

 * Lock, Shock and Barrel - Spooks of Halloween Town
 * Oogie Boogie - Squirming Evil
 * Oogie's Manor - Destiny's Force

Neverland

 * AntiSora - Shrouding Dark Cloud
 * Captain Hook - Squirming Evil
 * Phantom - Destiny's Force

Hollow Bastion

 * Riku (1st Battle) - Scherzo Di Notte
 * Maleficent - Squirming Evil
 * Maleficent (Dragon) - The Deep End
 * Riku (2nd Battle) - Forze del Male
 * Behemoth - Destiny's Force

End of the World

 * Chernabog - A Night on Bald Mountain (Squirming Evil in original Japanese version)
 * Ansem, Seeker of Darkness (1st Battle) - The Deep End
 * Darkside - Destiny's Force
 * Ansem, Seeker of Darkness (2nd Battle) - Forze del Male
 * World of Chaos - Guardando nel buio

Hollow Bastion

 * Unknown - Disappeared

Traverse Town

 * Guard Armor - Struggle Away

Wonderland

 * Card Soldiers - To Our Surprise
 * Trickmaster - Struggle Away

Olympus Coliseum

 * Cloud - Face it! (Go for it! in PS2 remake)
 * Hades - The Fight for my Friends

Agrabah

 * Jafar - The Fight for my Friends

Monstro

 * Parasite Cage - Struggle Away

Halloween Town

 * Oogie Boogie - The Fight for my Friends

Atlantica

 * Ursula - The Fight for my Friends

Neverland

 * Captain Hook - The Fight for my Friends

Hollow Bastion

 * Maleficent - The Fight for my Friends

Destiny Islands

 * Darkside - Struggle Away

Twilight Town

 * Vexen (2nd Battle) - The 13th Struggle

Castle Oblivion

 * Axel (1st Battle) - The 13th Struggle
 * Larxene (1st Battle) - The 13th Struggle
 * Riku Replica (1st Battle) - The Force in You
 * Riku Replica (2nd Battle) - The Force in You
 * Vexen (1st Battle) - The 13th Struggle
 * Riku Replica (3rd Battle) - The Force in You
 * Riku Replica (4th Battle) - The Force in You
 * Larxene (2nd Battle) - The 13th Struggle
 * Axel (2nd Battle) - The 13th Struggle
 * Marluxia (First Form) - Graceful Assassin
 * Marluxia (Second Form) - Scythe of Petals

Hollow Bastion

 * Maleficent - The Fight for my Friends

Traverse Town

 * Guard Armor - Struggle Away

Agrabah

 * Jafar - The Fight for my Friends

Monstro

 * Parasite Cage - Struggle Away

Neverland

 * Captain Hook - The Fight for my Friends

Wonderland

 * Trickmaster - Struggle Away

Olympus Coliseum

 * Hades - The Fight for my Friends

Atlantica

 * Ursula - Face It!

Halloween Town

 * Oogie Boogie - The Fight for my Friends

Destiny Islands

 * Darkside - Struggle Away

Twilight Town

 * Riku Replica (2nd Battle) - The Force in You

Castle Oblivion

 * Vexen - The 13th Struggle
 * Riku Replica (1st Battle) - The Force in You
 * Lexaeus - The 13th Struggle
 * Ansem, Seeker of Darkness - Revenge of Chaos

Castle Oblivion

 * Marluxia (Third Form) - Lord of the Castle

Destiny Islands

 * Zexion - The 13th Struggle

Awakening

 * Twilight Thorn - Tension Rising

Simulated Twilight Town

 * Axel (1st Battle) - The 13th Struggle
 * Axel (2nd Battle) - The 13th Struggle

Hollow Bastion

 * Demyx (2nd Battle) - The 13th Dilemma

Radiant Garden

 * Sephiroth - One-Winged Angel (from Final Fantasy VII)

Land of Dragons

 * Shan Yu - Vim & Vigor
 * The Mysterious Man - The 13th Struggle
 * Storm Rider - The Corrupted

Beast's Castle

 * Possessor/Thresholder - Dance to the Death
 * The Beast - Tension Rising
 * Shadow Stalker - Dance to the Death
 * Dark Thorn - Desire for All That Is Lost
 * Xaldin - The 13th Dilemma

Underworld

 * Cerberus - Vim and Vigor
 * Demyx (1st Battle) - Tension Rising
 * Pete (1st Battle) - Rowdy Rumble
 * Hades - The Encounter

Olympus Coliseum

 * Hydra - Desire for All That Is Lost

Timeless River

 * Pete (Timeless River) - Rowdy Rumble
 * Pete (2nd Battle) - Rowdy Rumble
 * Pete (3rd Battle) - Desire for All That Is Lost

Port Royal

 * Captain Barbossa and Illuminator - Vim and Vigor
 * Grim Reaper (1st Battle) - Sinister Shadows
 * Grim Reaper (2nd Battle) - The Corrupted

Agrabah

 * Volcanic Lord and Blizzard Lord - Desire for All That Is Lost
 * Jafar - The Encounter

Halloween Town

 * Prison Keeper and Lock, Shock and Barrel - Dance to the Death

Christmas Town

 * Oogie Boogie - The Encounter
 * Lock, Shock and Barrel - Rowdy Rumble
 * The Experiment - The Corrupted

Pride Lands

 * Shenzi, Banzai, and Ed (1st Battle) - Rowdy Rumble
 * Scar - The Encounter
 * Shenzi, Banzai, and Ed (2nd Battle) - Rowdy Rumble
 * Groundshaker - The Corrupted

Space Paranoids

 * Hostile Program - The Corrupted
 * Sark - Sinister Shadows
 * Sark and the MCP - The Encounter

Castle that Never Was

 * Xigbar - The 13th Dilemma
 * Luxord - The 13th Struggle
 * Saïx - The 13th Dilemma
 * Xemnas - Disappeared
 * Xemnas (Dragon) - Fight to the Death
 * Xemnas (Dragon) (2nd Battle) - Darkness of the Unknown
 * Xemnas (Final) - Darkness of the Unknown

Kingdom Hearts

 * Xemnas (Armor) (1st Battle) - A Fight to the Death

Keyblade Graveyard

 * Lingering Will - Rage Awakened

Cavern of Remembrance

 * Roxas Data - The Other Promise
 * Larxene Data - The 13th Reflection
 * Marluxia Data - The 13th Reflection
 * Luxord Data - The 13th Struggle
 * Demyx Data - The 13th Dilemma
 * Axel Data - The 13th Struggle
 * Saïx Data - The 13th Dilemma
 * Zexion Data - The 13th Reflection
 * Lexaeus Data - The 13th Reflection
 * Vexen Data and Anti Form - The 13th Reflection
 * Xaldin Data - The 13th Dilemma
 * Xigbar Data - The 13th Dilemma
 * Xemnas Data - Disappeared/Darkness of the Unknown

The World that Never Was

 * Roxas - The Other Promise

Agrabah

 * Vexen's Absent Silhouette and Clone Sora - The 13th Reflection

Twilight Town

 * Lexaeus's Absent Silhouette - The 13th Reflection

Underworld

 * Zexion's Absent Silhouette - The 13th Reflection

Beast's Castle

 * Marluxia's Absent Silhouette - The 13th Reflection

Port Royal

 * Larxene's Absent Silhouette - The 13th Reflection

Twilight Town

 * Guardian - Tension Rising
 * Veil Lizard - Shrouding Dark Cloud
 * Tailbunker - Tension Rising
 * Darkside - Destiny's Force
 * Powered Armor - Tension Rising
 * Dustflier - Fight and Away
 * Xion: Final Form - Vector to the Heavens

Agrabah

 * Pete - Rowdy Rumble
 * Antlion - Shrouding Dark Cloud
 * Xion: Third Form - Fight and Away

Beast's Castle

 * Dark Follower - Destiny's Force
 * Infernal Engine - Vim and Vigor

Olympus Coliseum

 * Morning Star - Tension Rising
 * Xigbar - Rowdy Rumble
 * Guard Armor - Shrouding Dark Cloud

Wonderland

 * Lurk Lizard - Tension Rising
 * Crimson Pranksters - Fight and Away
 * Xion: First Form - Shrouding Dark Cloud

Neverland

 * Wavecrest - Tension Rising
 * Ruler of the Sky - Fight and Away

Halloween Town

 * Lock, Shock and Barrel - Spooks of Halloween Town
 * Leechgrave - Vim and Vigor
 * Xion: Second Form - Vim and Vigor

Castle That Never Was

 * Saïx - Critical Drive

The World That Never Was

 * Riku - Another Side -Battle Ver.-

Land of Departure

 * Master Eraqus - Terra
 * Unknown - Dark Impetus

Enchanted Dominion

 * Maleficent - The Encounter
 * Maleficent (Dragon) - The Encounter
 * Wheel Master - The Tumbling

Dwarf Woodlands

 * Magic Mirror - Vim and Vigor
 * Mad Treant - Unforgettable

Castle of Dreams

 * Symphony Master - The Tumbling
 * Lucifer - Rowdy Rumble
 * Cursed Coach - Extreme Encounters

Radiant Garden

 * Trinity Armor - Unforgettable
 * Braig - Black Powder
 * Terra-Xehanort (Last Episode) - Dismiss
 * Vanitas - Enter the Darkness

Olympus Coliseum

 * Hades and Ice Colossus - Destiny's Force
 * Zack - Shrouding Dark Cloud/Extreme Encounters

Deep Space

 * Experiment 221 - Vim and Vigor
 * Gantu - The Encounter
 * Metamorphosis - The Tumbling

Neverland

 * Peter Pan - Vim and Vigor
 * Captain Hook - The Encounter
 * Vanitas - Enter the Darkness

Keyblade Graveyard

 * Master Xehanort and Vanitas - Black Powder
 * Master Xehanort - Black Powder
 * Terra-Xehanort - Rage Awakened -The Origin-
 * Braig - Another Side
 * Vanitas - Enter the Darkness/Unbreakable Chains
 * Ventus-Vanitas - The Key
 * Vanitas Remnant - Enter the Void

Realm of Darkness

 * Unnamed Heartless - Hunter of the Dark

Mirage Arena

 * Iron Imprisoner I, II, III and IV - Unforgettable
 * Mimic Master - Unforgettable
 * Monstro - Monstrous Monstro -Arena Ver.-
 * Armor of the Master - Master, Tell Me the Truth
 * No Heart - Forze dell'Oscurita

Destiny Islands

 * Tidus - Destiny Islands
 * Darkside - Destiny's Force

Traverse Town

 * Guard Armor - Shrouding Dark Cloud

Wonderland

 * Trickmaster - Tension Rising

Olympus Coliseum

 * Cloud - Go for It!
 * Cerberus - Fight and Away
 * Hades - Vim and Vigor
 * Rock Titan - Fight and Away
 * Behemoth - Fight and Away
 * Ice Titan - Fight and Away

Agrabah

 * Jafar - Fight and Away
 * Jafar (Genie) - Vim and Vigor

Hollow Bastion I

 * Pete - Rowdy Rumble
 * Data-Riku - Riku

Hollow Bastion II

 * Data-Riku - Riku
 * Maleficent (Dragon) - Vim and Vigor
 * Sora's Heartless: Neo Darkside - Destiny's Force
 * Sora's Heartless: True Form - Guardando nel buio

Castle Oblivion

 * Tidus - Forgotten Challenge
 * Pete - Forgotten Challenge
 * ??? - Roxas

Destiny Islands

 * Ursula - Night of Fate

Traverse Town

 * Hazokaru - Untamable
 * Julius - The Encounter

Country of the Musketeers

 * Beagle Boys and Pete - Rowdy Rumble