- Hammer Bro
- Waluigi
- Chain Chomp
- Thwomp
- Klaptrap
- Skull Kid
- Moon
- Midna
- Ghirahim
- Metroid
- Mother Brain
- Knuckle Joe
- Nightmare
- Chef Kawasaki
- Andross
- Krystal
- Jeff
- Starman
- Samurai Goroh
- Lyn
- Tiki
- Black Knight
- Phosphora
- Ashley
- Gray Fox
- Shadow
- Knuckles
- Burrowing Snagret
- Kapp'n
- Wily Capsule
- Zero
- Ghosts
- Riki
- Guile
- Rodin
- Squid Sisters
- Alucard
- Color TV-Game 15
- Sheriff
- Devil
- Takamaru
- Dr. Wright
- Flies & Hand
- Sable Prince
- Sukapon
- Isaac
- Starfy
- Nintendog
- Dr. Kawashima
- Vince
- Dillon
- Yuri Kozukata
- Arcade Bunny
- Spring Man
- Bomberman
- Akira
- Rathalos
- Thwomp
- Moon
- Samurai Goroh
- Phosphora
- Knuckles
- Rodin
- Color TV-Game 15 (the only Assist Trophy without a Spirit to begin with)
- Sheriff
- Starfy
- Rathalos (on account of being a proper boss)
I'd much rather have X9 developed by Capcom themselves-and preferably along the lines of Mega Man 9, a faithful continuation with an SNES artstyle.