What are your favorites and if you can tell why, that's even better. Castlevania or otherwise.
https://www.youtube.com/watch?v=dCpL1Sa5pBE
The first one (Castlevania) is one of my favorite among CVs, with Dracula's Curse's triumph fanfare a close second. Not just because of nostalgia. I like how they're variations of the normal stage clearing theme with more bravado. In normal stages, there's the kind of tone that tells it's not over yet. But with that theme that plays when you pick up that final energy crystal..man, it's like you just conquered the world and lit up a cigar using a flaming body part of your worst enemy 8)
Chronicles and SCVIV have more poignant ones, but still with a "you earned this victory" kind of vibe.
Gunstar Heroes has a chneerful jingle when a stage is clear, Dynamite Headdy also from Treasure also has a nice stage clear jingle to it that is quite cheerful. Ristar I also love the stage clear theme from as it isn't short.