Board Thread:Questions and Answers/@comment-27598407-20160206111656/@comment-78.20.131.40-20160206130006

It differs from MG to MG. These are the more conventional ones:

Succubi, Mammal Beastmen, etc. all give live birth just like humans do.

Avian, Reptillian & aquatic beastmen lay eggs.

Slimes through mitosis.

Plants like Alraune and Mandragora spread out seeds or spores.

There are also some unconventional ways, mostly the parasitic and artificial mamono, but pretty much all of them can reproduce like the above as well.

As for the belly buttons, well mamono are partially human and are supposed to be attractive to humans. So even those who don't need it shall have it for aesthetic purposes.