I'd like to thank my buddy who lives with me for helping me out on quite a bit on the casing and advicing.
Then I'd also like to thank [mention]kite[/mention] for his support on my battery monitor.
Credits to [mention]helder[/mention] and [mention]wermy[/mention] for their ideas and existing products which I very basic reproduced (I always wanted to order an AIO from [mention]helder[/mention], but never gotten the chance to as everytime I checked it went out of stock

I had a lot of fun building this project and gathered quite a bit of experience, and that is what counts, right?

The end product is not "perfect", but in no way was it ever meant to be.
Here are pcitures of the finished result:





----------------------------------------------------------------------------
Original posts starting from here ->
----------------------------------------------------------------------------
After seeing all parts of [mention]Wermy[/mention]'s video guides I fell in love with the end result and decided to make my own, though I want to make it a little individual.
Now, I am not going to modify an existing Game Boy. I am going to start from scratch with an aftermarket case in transparent blue, like this one here:

- - Instead of using an RPi Zero, I want to actualy use an RPi 3 for more capabilities such as more compute power, wifi and bluetooth etc. which I have sucessfully modified in order to fit into an actual gameboy (desoldered pretty much every IO except for µUSB)

Just to clarify things, they are 100 % intact. What you are seeing is the pure copper, and yes, there was no solder/not much solder on them, that is the reason they look sort of brown-ish instead of silver like solder would.
On the underside of the board, you see that things do look different.

To make sure it still works, I attached the Pi to my TV via composite over those pins (Audio and Video, pads marked in red circles) and my PC also discovers it over WiFi (\\retropie)

Now, I took my girlfriends existing gameboy apart (which I won't sacrifice for this project) to see how well the Pi could fit inside, and it didn't look like it's going to give me trouble, but we'll see about that in the future

- - Having two analog sticks from a PSP 1000 inside to use other/more emulators (e.g. N64, PSP of course)
- Instead of just having L and R buttons, I am going to add L1, L2, R1 and R2 so that you can for example play PS1 games.
Now, I first have to order these and wait for them to arrive, but I will keep you updated!

UPDATE: Everything has arrived.

[spoiler="Parts list"]
- ARRIVED - Tri-Colour LED (RGB) for battery, charge and power indication
http://www.ebay.de/itm/172232033249?_tr ... EBIDX%3AIT - ARRIVED - Adafruit Powerboost 1000C
http://www.ebay.de/itm/282083284436?_tr ... EBIDX%3AIT - ARRIVED - USB Mini (rather than micro) Breakout
http://www.ebay.de/itm/282073486859?_tr ... EBIDX%3AIT - ARRIVED - Some random gameboy game to cover up
- My girlfriend gave me her old broken Tetris, which she had 2 of - - ARRIVED - Tactile switches
http://www.ebay.de/itm/291371993802?_tr ... EBIDX%3AIT - ARRIVED- 3 pin slide-switch
http://www.ebay.de/itm/140714113454?_tr ... EBIDX%3AIT - ARRIVED - a Leonardo micro instead of an Teensy (it's alot cheaper in germany)
http://www.ebay.de/itm/301951688967?_tr ... EBIDX%3AIT - ARRIVED - Volume wheel potentiometer
http://www.ebay.de/itm/322281495072?_tr ... EBIDX%3AIT - ARRIVED - 64 GB Samsung EVO micro SD card, which has been confirmed to work
http://www.ebay.de/itm/251970254487?_tr ... EBIDX%3AIT - ARRIVED - Common Ground DMG+ Control Panel with X, Y, L1 & L2, R1 & R2 from Kitsch-bent
http://www.ebay.de/itm/191968449407?_tr ... EBIDX%3AIT - ARRIVED - Gameboy classic buttons (2x)
http://www.ebay.de/itm/182258143348?_tr ... EBIDX%3AIT - ARRIVED- Gameboy Speaker
http://www.ebay.de/itm/181950378790?_tr ... EBIDX%3AIT - ARRIVED - Gameboy classic rubber pad set (2x)
http://www.ebay.de/itm/181814606804?_tr ... EBIDX%3AIT - ARRIVED - Spare USB ports (2x)
http://www.ebay.de/itm/130707477798?_tr ... EBIDX%3AIT - ARRIVED - Headphone jack w/ switch
http://www.ebay.de/itm/161337167416?_tr ... EBIDX%3AIT - ARRIVED - Audio amplifier
http://www.ebay.de/itm/322283374092?_tr ... EBIDX%3AIT - ARRIVED - 3.5" TFT screen w/ controller
http://www.ebay.de/itm/162128950289?_tr ... EBIDX%3AIT - ARRIVED - Complete gameboy classic shell
http://www.ebay.de/itm/331975728644?_tr ... EBIDX%3AIT - ARRIVED - 2500 mAh 3.7V battery
http://www.ebay.de/itm/391585262102?_tr ... EBIDX%3AIT - ARRIVED - PSP analog stick (2x)
http://www.ebay.de/itm/361351958328?_tr ... EBIDX%3AIT
Also I made a little (and very rubbish) "concept" of what it could look like in photoshop ^^'':

(Front only for now)
Also, the analog stick's positions aren't definite right now, but I grabbed my gameboy and imagined analog sticks to be there and then I came up with the center and a little higher than the left bottom to be comfortable spots.
The 4 raspberries only showcase it to be an RPi with 4 CPU's, in this case an RPi 3.