Mario & Luigi RPG 5: The Dark Doppelganger (Early WIP, tentative title)

So I started this project a few months ago, and with the release of Mario Kart 8 I kinda dropped it for a while. But now I'm going to try to get back to working on it. Here's the latest demo I have released: https://www.mediafire.com/?dfry92x5d9d12h1

I kinda suck at creating stories, I know the evil doppelganger thing is cliched but it's seriously the best thing I could think of...for now, at least. I'm still a noob at RPG Maker VX Ace so any pro tips would be appreciated. Enjoy the demo!

Edit: Almost forgot the credits:
Croshi
Crazy Koopa
MGZE
A.J. Nitro
Lemon
Ragnarok
Sphacks
puggsoy
Luigirulz
KingAsylus91
Ninboy123
Brawlfan1
Tero
DarkBlade2
Yanfly
Galv
Jet
Pacman
Lakituthequick (Fawful mugshot)
Me (Dark Mario mugshot, Beanish Guy Mugshot)
Nintendo (Other mugshots; original sprites and music)
Square-Enix (SMRPG battle theme)