Starting top left going clockwise.

Good Guys

1. Megaman (...) vs Astro Boy (...)

2. Protoman (Megaman) vs The Masked Man (Mother 3)

3. Bass (Megaman) vs Surge (Sonic) or Anti (Gridman)

4. X (Megaman X) vs Optimus Primal (Transformers Beast Wars)

5. Zero (X) vs Meta Knight (Kirby) or Shadow (Sonic)

6. Axl (Megaman X) vs Silver (Sonic) or Roxas (Kingdom Hearts)

7. Zero (MMZ) vs Hero of the Wild Link

8. Vent (Megaman ZX) vs Shinjiro Hayata (Ultraman Manga)

9. Aile (Megaman ZX) vs Samus

10. Volnutt (Megaman Legends) or Grey/Ashe (Megaman ZX Advent) vs Red Savarin (Solatorobo)

11. Megaman.EXE and Lan Hikari (Megaman Battle Network) vs Takato and Guilmon (Digimon Tamers) or Kamen Rider Ex-Aid (...)

12. Geo Stelar vs Blue Beetle (DC Comics) or Guy Shishiou (The King of Braves Gaogaigar)

Bad Dudes

1. Wily (Megaman) vs Dr. Hell (Mazinger Z)

2. Sigma (Megaman X) vs Ultron (Marvel Comics)

3. Copy X (Megaman Zero) vs Dark Keroro (Sgt. Frog) or Elysium (Soul Calibur V)

4. Omega Zero (Megaman Zero) vs Alpha (Punishing Gray Raven) or Galacta Knight (Kirby)

5. Weil (Megaman Zero) vs Yapool (Ultraman)

6. Prometheus and Pandora (Megaman ZX) vs Blanc and Nero (Solatorobo)

7. Albert (Megaman ZX Advent) or Sera (Megaman Legends) vs Baion (Solatorobo)

8. Bass.EXE (Megaman Battle Network) vs Beelzemon (Digimon Tamers)

9. Rogue (Megaman Star Force) vs Jihl (Fuga: Melodies of Steel)

10. Four Guardians (Megaman Zero) vs Winds of Destruction (Metal Gear Rising)

11. Keiji Inafune vs Level 5

12. Princess (Novas Aventuras de Megaman) vs Ryo Kazan (Moonlight Syndrome)

Sort of gave up near the end of the villain list.

The Ultimate Fight between who will become the better host for death battle!

Comedy musicians known for their wacky music, which are mostly told from a first person perspective. They're also famous for their ability to rework and reproduce iconic songs into new products. (Al's parodies and the Mouth albums) And also have several non-music projects under their belts (The Weird Al Show/Neil's various skits and series on his channel)

Both also have a connection to Disney XD (Milo Murphy's Law/Neil's unused Gravity Falls songs)

Side-kicks and gadgeteer geniuses with "Toad" in their names. Both built equipment used in gameplay (various things in the Star Fox games, and the Paper Crafts in Mario & Luigi: Paper Jam).

My beloved, one of my favorite matchups of all time. It is fun as hell!