There are many ways to create a mini. Here's one of them.
For this rendition, I chose a neck on which the fingerboard had delaminated almost 1/3 the way. It was easy to peel it off the rest of the way with a putty knife.
The idea is to use the smaller part of the scale. I played a trick here by adding the big frets back at the top, but I needed to cover up the truss rod with something.
It's a Strat style floating tailpiece locked down in such a way as to direct the break angle pressure through a piezo transducer embedded under the bridge.
Built inside the amp case is an end pin style piezo preamp that disconnects with the same switch that shuts the power amp down.
As one might imagine, this configuration created a seriously bright tone, so I addressed this issue on two fronts. First, I changed out the strings with some very fine viola and violin strings. Not only are these strings gentle on the fingers, they are warmer sounding and have depth in their character. The other way we handle the brittle nature of the tone derived from piezos was to add an extra tone knob with doubled up caps welded to it so you can roll it way back if you like.
The body is from an old heavy metal 5-string bass. It's part of the lower cutaway horn.
The amp is from a Fender® MD-20 and it runs on a 9v. battery. Vol. Tone. Gain. I recommend Lithium rechargeable for the obvious reason, of course, but above all, the tone is far superior.