Smash 4 Automatic Custom Farming Guide
Smash 4 Automatic Custom Farming Guide by Dunnobro
You will need a turbo enabled controller for this to work
Go make a tag, then set the controls for that tag so the A button is set for specials. (Strongly recommended you also turn off rumble)
Go to target blast, stage 2 with Ganondorf.
Turn Turbo on for the A button, and fashion it so it’s pressed down. (Tape, rubber band, weight, lots of ways to do it)
He will automatically punch the bombs, which will always blow up all but two targets. I’m not 100% sure on the logistics, but it seems like the wrenches can spawn at any target. Meaning that’s only a 1/14 chance ganon will miss the custom.
After that, he will re-enter endlessly and do it over, and over again since it’s all progressed by hitting the A button.
Also not sure how often they come out on their own, at worst though it seems like 1/5 of each target blast shows a custom.
With about 30 seconds per target blast, that should be 1 custom part every two and a half minutes.
Edit: For more optimal results, play with characters that have fewer customs in other game modes after a bit of those, to give preference to them and avoid duplicates more efficiently.
Check out this guide for further speeding up.