Soft plastics!
I have a number of injection mold files I've designed. Trickworms, senkos, grubs, ribbon tails, frog, beaver style bait, ned, and probably a few i cant think of right now.
You have to print in PETG. PLA does not have the temperature resistance.
Because of the layer lines, it can be difficult extracting the baits, so you need to use some sort of mold release. I used vegetable oil. You lose some details because of this when compared to aluminum, or composite molds.
It is fun though, designing your own lures and seeing them come to life.
Ive found that buying aluminum molds is worth it though, if you're willing to put up the money. The detail is just much better, and many molds are very affordable.
I have several do-it molds now, and some cheap amazon composite molds as well. Those just shoot much better.
Printed a whopper plopper too. It worked pretty well.
I use my printer for other fishing related things too. Right now I'm printing a handle for a diy stake out pole. They're very useful.