More Songs just if you want to know. These are probably obvious and some are not. Depends.
Volibear: AC/DC-Thunderstruck
The Rock : Apollo 440-Can't Stop the Rock (Well what a surprise)
Evil Pumpkin: In The Hall of the Mountain King (Techno Remix)
Happy Mask Salesman: Literally the bgm is his name.
Spongebob: Goofygoober
The Invisible Man: Scatman John-Invisible Man
Garfield: Garfield and Friends Theme Song-Ready to Party
The Real Jason Voorhees: Saw Intro Song-Hello Zepp (I don't know if it was Michael Myers though)
Rage Sniper: F***ing Guile's Theme
Willy Wonka: Sammy Davis, Jr - The Candy Man Can
Freddy Fazbear, Chica, Foxy: The Living Tombstone - FIVE NIGHTS AT FREDDY'S SONG! (apparently a very requested question for these bosses so here's your answer)
Zombie: Michael Jackson-Thriller (well...)
Bob The Builder: Series Theme Song
Kermit: Sesame Street Song (1998-2001 version)
Metal Mecha Bowser: Mecha-Bowser-Super Mario Sunshine (composer: Shinobu Tanaka)
Demo Samedi: King Diamond-The Cross of Baron Samedi
Alien (or Alien Queen idk): ZZ Top-Gimme All Your Lovin'
Bart Simpson: Bart Simpson Rap
Evil Homer Simpson: The Simpson Theme Song
Ghostbuster Spencer/Weasel Cake: Ray Parker, Jr-Ghostbusters
Capitan Falcon: Mute City (not sure which version but definitely not SNES one)
Sonic.exe: Sonic.EXE Hill Theme
Meet the Pyro: Do You Believe in Magic-The Lovin' Spoonful
Kirby: Green Greens Theme
Cristian Brutal Sniper: Combustible Edison-The Millionaire's Holiday
Pink Panther: Pink Panther Theme Song
Donkey Kong: Donkey Cong: Country Theme Song
The Candy Man: Aqua-Lollipop
Aaaaand those are the once that I know.