My favorite thing to do is to play Dr Frankenstein and cut up minis and reposition them to make totally new things from them. I use boxes of spare parts, 2 part epoxy putty (Kneadatite or "greenstuff" and Pro-Create), wire, tubing, and even bits of Lead Foil from old wine bottles. Sometimes I even use organic bits.
Conversion usually starts with a need for a miniature that does not as of yet exist. I will have customers describe for me what their hoped for outcome will be. Some conversions are minor. Add more hair or a beard Can you switch the sword out for a hammer. Add or delete a shield or swap heads are all pretty easy. This is a miniature I made for a player in one of my RPGs. She had acquired a set of magic bracers and collar that allowed her to transform into a dire wolf. I used a Reaper “Moor Hound” to start the process…