he can send ppl to the neather realm with his aura, he's protected by the orochi power since he's a herald, he's most likely invunerable. shin would kill igniz, but a guy like mukai isn't getting harmed. would probably take a superman/goku caliber fighter to take him down.
Mukai was far easier tyo defeat than most SNK bosses to date... Igniz gave me more trouble...
And I can very well assure you that Mukai is not Invulnerable. And that full screen attack he does is not a Netherrealm attack neither. Akuma killed guys like Bison in single moves... I firmly beleive that Mukai would be defeated.
When he is beaten he gets up unscathed , cannon wise he is a powerful diety, gameplay wise SFA2 shin akuma would sodomize him and igniz. and his super that takes the whole screen takes you to the netherworld and turns you to stone if it isn't blocked. the raging demon wouldn't touch this guy.
Since when was the full screen attack considered a Netherworld attack? I know it turns you into stone temporarily, bt it's no different from Gill's Seraphic Wing...
Anyways, I am certain that Akuma's various landmass destroying techniques aould definitely kill him (Kongou Kokoretsu Zan, Misogi And Tenshou Kaireki Jin)