Josef Prusa's Pug Buddy Keychain
The original Pug Buddy from Josef Prusa. The only modification I made is to add a little part with a hole in order to attach a keychain. Unlike other designs, I sized the ring attachment so that it is sturdy and doesn't break easily. I then added a keychain I bought in a shop for about $1.50. Just bend it open, put it trough the hole, and bend it back straight.
You can scale it down to about 75% of the original size and a normal little ring (see picture) should still fit. The hole is 3mm.
I printed mine at 0.2 layer height and 10% infill, no supports needed.
You can edit the original file on Tinkercad.
The model is under CC BY-SA 3.0 licence.