I will either print the plastic automatas on a 3D printer, or you can also buy ready-made kits...
DOLPHIN
(3D print-automata)
Source: Briny
https://www.thingiverse.com/thing:13493
Video:
https://youtu.be/Ht9mPbxJ0jo
The automata has only a few parts, but it moves nicely ...