Model remixed from the Adafruit MagTag Case and Stand, and from https://www.thingiverse.com/thing:4815930

The Thingiverse model added cutouts for the STEMMA 3 pin JST connectors to the front cover, and the case frame. 

An eyelet was added to the case frame, where a lanyard can be attached, making it possible to use the MagTag as badge. 
The back cover leaves room for a LiPo battery, and it secures to the frame with 4 M3 screws, making the case nice and portable. 
The front cover printed in white / translucent PLA offers excellent diffusion for the Neopixels.