*cracks her knuckles* Let's done do this.
Death by Glamour (Undertale) - An amazing song in a soundtrack full of amazing songs, it's difficult to choose just one battle theme from Undertale - and let's be clear, the battle themes are where Undertale really shines. There isn't a battle theme in this game that isn't amazing, but I'm quite partial to this one just for its dance club vibe.
Calamari Inkantation (Splatoon) - Hey, do you like the music that plays whenever a Splatfest is going on? How'd you like it if we took that music and made it into a final battle theme? This one's pretty goofy, but also terribly catchy.
Victory in the Dream World (Mario & Luigi: Dream Team) - This game gets a lot of flak for a variety of reasons, but one way it stands out is its soundtrack. Not only is it the strongest soundtrack of the entire M&L series, it's also arguably some of the finest work Yoko Shimomura has done. It's lively, upbeat, and cheerful - but also still keeps that battle vibe. I never once got tired of it while playing through this game.
Xerneas and Yveltal (Pokemon X & Y) - Second best battle theme in the entire Pokemon series, beaten only by...
Miror B.'s Disco Groove (Pokemon XD) - ...this one. They need to get this composer doing work for the main series Pokemon games.
Discussion -HEAT UP- (Danganronpa) - The song that plays whenever the trial gets to a fever pitch. It doesn't sound like what you'd think a trial should sound like, but that's okay; it matches Danganronpa's fast pace and tense atmosphere to a T.
Burden of the Son (Final Fantasy XIV) - A boss battle theme inspired by old-school sentai music, which makes sense when you realize that the boss itself is inspired by old-school sentai. Cheesy, catchy, and heavy on the brass - what's not to like?
The Last Time Travel (Professor Layton & the Unwound Future) - I'm not crying, you're crying! I'm just... peeling onions. For my dinner. That I'm having. Tonight. Shut up!
The Little Bonus Room (Skullmonkeys) - Just... listen to it. You'll see why.