regarding the third parties second character:
Sonic: Eggman, there seems to be a conscensus regarding eggman being amazing, but seriously, a well written eggman is such a fun villian.
Megaman. Zero (advance version) i always liked this design, and the gameboy advances games were quite solid... and i certainly enjoyed the story there, Plus, Xs zero is overrated, while we can have a full protagonist Zero
Snake: Rayden I agree with this one, rayden isnt the terrible character some people think it is, and is a great counterpart to snake.
Pacman: no idea... maybe pacman franchise could be considered namco arcade classics, and teh secon character could be another namco's arcade classic such as Dug Dug?
Ryu: Chun-li almost as iconic. and while she would share some mechanichs with ryu, she is a completely different character
Cloud: Torn between Terra and black mage, I will go with terra due to the chance of a final fantasy VI stage
Bayonetta: certain lumen sage. I loved this character in bayonetta 2 and i love how he compliments bayonetta in such a taoist way. Jeanne and Rodin are all cool but the walking spoiler gets my vote.
Simon Belmont: Alucard. wait... you say that simon is still not confirmed? daaaaaamns!