That'd be cool, but then we wouldn't be able to see Monster Luffy kick Moria's butt. So unless they make it happen after Luffy gives Moria a good beating, then that'll be no fun. Moria is one annoying SOB and just like Spandam in Enies Lobby, I am looking forward to Moria taking a severe beating.
Actually I think that it would be pretty dull if Luffy would still be in Nightmare mode when he´s fighting Moria. If that happens you could never erase the thought that Luffy couldn´t beat Moria without additional help which somehow sucks IMO. For Odz it is ok, because that monster is a totally different world but Moria who bounty-wise is in the same league as Luffy should be defeated by Luffy alone without the help of spirits of other people.
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But then, i was thinking that Moria is the smart sort, so he'd phrase his words properly (unlike dimwit "genius" fosfos guy)
IMO, that was one of the weakest parts of ALL of One Piece. I´m still having a tough time to swallow that Oda really put those words in Robins mouth to trick Hogback. I mean even the stupidest members on this board wouldn´t have fallen for that one.
But nevermind, if that trick would really be used against Moria, then it would be somehow with him noticing it anyway because I doubt that he has a voice that loud that it could be heard over all of Thriller Bark. So an hidden mic or something like that could do the trick (perhaps with the help of Nami and Usopp) while Moria thinks he only talking to Nightmare Luffy.