Online play? YES!
Here is a co-op Boss Fight of my Avengers United Battle Force, played by me (Brand, Brazil) and my good friend Psykai (Iron man, UK) using Parsec.

http://www.youtube.com/watch?v=EZBD_-BJNjA&feature=youtu.be

We had a little lag thanks to the distance, but its quite playable!
Works with Mugen too.

========= LINKS ========

Download Parsec: https://parsecgaming.com/
Configuration tips: https://www.youtube.com/watch?v=OifIGIvhjb8
Discord channel for OpenBOR matches: https://discord.gg/fXQFNsE

Download Avengers United Battle Force FOR FREE. It runs on Windows, Android and Linux - http://www.brazilmugenteam.com/avengers