My son turned 16 and loves Mcgybeer's "Articulated Shark."  So I made him a keychain version of the model. 

I scaled the design and added a loop to attach your keys to.  I also attached the tail to the last body segment and made it so that it prints vertically as at the half scale I could't get the tail's ball joint to work. All the other joints worked though, which I was a touch surprised at.

It prints beautifully on my Prusa MK4.

I have collection of keychains which include more of McGybeer's designs if that is more up your alley.