I recently got the idea to make a smaller iTapStick. The iTapStick is a Wii Nunchuck that is a mouse using USB: https://learn.adafruit.com/nunchuket-ku ... y?view=all
The way I would make it smaller is put the Pro Trinket inside the Wii Nunchuck, not as a separate board the Nunchuck plugs into. I call it the USBChuck.

The Nunchuck is surprisingly empty, and has just enough space for a Trinket...

However, there is lots of support structure that gets in the way of the Trinket. I will have time to cut the support structure in a few days.

I checked the printed labels on the board for the wires, and despite the confusing wire colors (red for ground? What were they thinking?) they are correct. My wirings are as follows:
Red --> A2
Green --> A3
Yellow --> A4
White --> A5
Black --> NC

I have no idea what the black wire does.

I made some simple cuts of the support structure, and soldered the wires from the Nunchuck to the Pro Trinket. I also had to cut some of the casing off of my USB cable. Then, I added Sugru to hold things together and to protect the wires. I also put electrical tape on the end of the mystery black wire and left it in the Nunchuck.

Now time for the code!
I have been modifing the iTapStick code from Adafruit. So far I have made the mouse easier to control, and added click-and-drag. Soon, I will add basic acceleration. Here is my modified code: