User blog comment:MrPacheco101/Rework Part 3: Spawn (Al Simmons) vs. Devilman (Akira Fudo)/@comment-11320328-20130627132307/@comment-1295722-20130706123759

If you don't believe me about his ability to turn humanity into puddle, read the manga "http://gonagai.wikia.com/wiki/Amon:_The_Darkside_of_The_Devilman" or just go to this link to expand your research and resources.

to summerize it short, Akira loses his ability to control amon once seeing miki decapitated, (which if you remember clearly from the begining, the only way he could have controlled amon was from his purity which ryo knew and recommended akira to merge with amon) well from miki's death, he lost his humanity and in a sense, lost control of amon which possesed his body and went on a rampage until he was confronted again with amon and they both faught. Psycho Jenny, the follower of Satan, aka ryo brainwashed humanity into killing each other to pave the way for the demon invasion, in the process making amon taking full control of akira.

you can look at other abilities that I haven't mentioned if you do decide later on to do a future match up using devilman.

http://www.mangahere.com/manga/neo_devilman/v03/c006/11.html