No order to them. Spoilers about some of the games ahead I guess. You've been warned.
1.
Valkyrie Profile: Covenant of the Plume - An Abyss of Niflheim If you managed to finally get through this game and receive the best ending (kill none of your teammates, you almost need to get the other two endings first so you have more abilities at hand), you get this music during the boss fight against Ailyth. You finally get to whip that smirk off of her face...and she changes into a huge demon dog, complete with cutscene of her transforming, smirking the whole time.
Oh dear. (watch at the 1:55 point if you just want the transformation, and not the reason why you should hate her.)
2.
Sonic the Hedgehog (2006) - His World (Zebrahead Version) Something good about Sonic '06? Blasphemy! Well, I happen to like some of the music from that game. Brawl has the instrumental version of His Word (Crush 40 Version). I happen to prefer the Zebrahead version for some odd reason. Sue me. I like the faster pace of it compared to Crush 40's verison.
3.
Fire Emblem: Path of Radiance: Ashnard's Battle Theme Given how little he thinks of everyone, wastes lives, and how much he only cares about power in FE9, I just love this theme. It seems to fit him very well, and I love the feel it gives to the last battle. I generally love the final boss themes in the Fire Emblem series, but this one is my favorite. It should have been in Brawl instead of that stupid Oliver theme. Too bad you don't get to hear much of it in game, you're too busy aethering him to death.
4.
Tatsunoko vs Capcom - Burning Wasteland Screw Orbital Ring, this song is where it's at. Much more epic feeling, and frankly fits a fighting game better. Casshern in general has better music for his stages than the other characters.
5.
Custom Robo - Forest of Nostalgia The first time you hear this song in particular is eery. You've just found out everything you knew was a lie. The world used to be a bigger than the dome you know. It's so big, it's actually round! But an entity known only as Rahu destroyed the vast, vast majority of humanity, leaving only a barren wasteland behind him. Whatever the being was, it was a silent, invisible, lethal force bend on destroying all humans, and their word. The only reason
humanity still exists is because he managed to trap himself inside of a child's toy: a Custom Robo. He was then defeat, and kept asleep since then, with everyone's memories of the outside erased. Oh, and by the way, that strange robo you just battled with that weird stage where the grass and trees felt more real (as all real trees and grass were destroyed) was Rahu. He's awake, and regaining his power. Have fun.
BTW: I hate you TC for only allowing 5 songs.