I have heard that only the undiscovered egg group can't breed. Since magneton is in the mineral group, can it breed with a ditto?
Yes, it can breed with a Ditto. Every Pokemon except ones in the Undiscovered egg group can breed with Ditto.
Yes, it can. Genderless Pokemon's Egg Group don't matter at all since Ditto is the only Pokemon that they can breed with.
Source: Experience
Yeah, Mageton can breed with ditto. All Pokemon that are not in the undiscovered egg group are eligible to breed with ditto. All other Pokemon can breed with ditto, even if it doesn't have a gender.
Yes, it can breed with Ditto.