Dude, what you've done here is incredible!
I was a huge fan of the mystery dungeon series, but I have yet to buy a 3ds, so I haven't gotten to play GTI. I'm glad to hear from this that the music is as inventive and atmospheric as from the previous games (Those games, musically speaking, are actually a huge inspiration to me). I wish I'd heard the original to have more context into what you've changed here, but since you didn't compose the music, I'm only going to review your production technique etc.
First off, I love just how spread out over the stereo spectrum this is, right from the get go. It really envelopes the listener, draws them into the track and fills them with a sense of wonder. At about 0:24, I was afraid it was going to turn into a generic dubstep remix, but it went right back into that same chill groove. A musical bait and switch, and one that works really nicely! I'd say that maybe the kick/snare is a little too heavy here, but that's just a matter of taste.
At 0:39, I LOOOVE the way you mixed this counter-line on synth harp. Both it and the melody are beautiful, and because of your mixing choices I'm able to not only focus on both lines at once, but appreciate the way they interact with one another.
Great job on the smooth tempo change at 1:03! To my taste, the lead synth is just a little too grating. Don't get me wrong, I love that square wave sound, but I might have added the tiniest bit of low pass on it. Just a minor nitpick, though, and it doesn't both me very much at all until 1:22. There, you should at the very least turn the volume down a little.
Transition at 1:28 is quite nice.
At 1:59, your choice to use a subtle electric bass-esque synth (it may actually be an electric bass for all I know lol) really pays off. It's a decision that truly marks this as something made by a mature producer, and I truly appreciate it.
2:20 or thereabouts, I very much enjoy the tone of the pad you have playing in and out of the background. This section shows a clear understanding of volume modulation and the ability to manage multiple textures at once (something I'm still working on haha).
Just a general note, the drum fills that you create in various areas are a really nice touch. I also love, love, love your use of the percussion toys you mentioned at the bottom of your description.
The return to the original groove/melody at around 2:40 (albeit modulated to a different key) is so satisfying, not only because of the transition, but because you took the time to create subtle differences between this and the beginning. It's familiar, but there's a lot of new stuff to listen for too. Again, this kind of thing is truly the mark of a mature, developed, well-practiced electronic composer.
The piano at 4:09 melts my heart. It sounds like you recorded it live (again, for all I know, you very well might have). Just gorgeous.
This review has gotten really long, and filled with a lot of gushing. What can I say? This is a superbly arranged, beautifully mixed, expertly produced remix.
Aside from my couple minor nitpicks, this is pretty much perfect.
Really well done.