As the tradition goes, a new and amazing version of Dearly Beloved just as beautiful as all the others. Especially when it's played when Sora and Riku save Mickey in Symphony of Sorcery.
Xigbar's own leitmotif, debuting in this game. It's the Organization XIII theme, only with a faster rhythm - a waltz, to be correct - and a creepy violin theme playing underneath. This is meant to invoke an unpleasant effectnote the same effect as, for example, The Third Day in Clock Town; and while it'd be spoileriffic to say why, this theme fits Xigbar and Braig perfectly, summing up his prominent role in the formation of the rest of the Organization.
Link to All is very upbeat theme that very well emphasizes Sora's ability to link so many hearts.
"UNTAMABLE", the most recurring Dream Eater boss themes, gives off a fun fair vibe, inviting you to enjoy the fight, while being fairly epic! This is in contrast to a good part of the other KH boss themes which are usually ominous and foreboding, while being epic.
Ice-Hot Lobster, like many Dream Eater boss themes, invites you to just enjoy the fight and have fun!
Gigabyte Mantis gives a techno feel to the usual Dream Eater music, and works you up to excitement as you battle the boss!
While Chernabog kept "Night On Bald Mountain" as his boss theme in the international and Final Mix of Kingdom Hearts, Some argue that the version used is pretty much inferior to the original. Thankfully, 3D remade it into something much more awesome to listen too, and it makes the fight ten times more epic!
"L'Oscurita dell'Ignoto" is a truly amazing rearrangement of Darkness of the Unknown. The violin gives off a very ominous, urgent vibe which really suits the fact that it plays during the fight that shatters Sora's heart.
There's also "L'Eminenza Oscura", the new battle theme of Ansem, Seeker of Darkness. Interestingly, it's what's missing from the song that makes it creepier than previous remixes. It starts off much like the first game's final boss theme, but then shifts into part of "Dismiss", the song from Aqua's fight with Terranort. Except Terra's Theme is missing from this part of the song. There is also the second part of the song which plays during Ansem's second phase. With extra emphasis on the "Dismiss" part of the song.
"The Nightmare" and "The Dream". When the former comes up, you know that something bad is going to happen, and the latter is a soothing playful melody that calms your soul.