Yes, it has been stated that Mamono would masturbate if lonely and without a man. Though, of course, those with a husband would rather storm towards him at full speed as masturbation alone does in no concievable way compare to sex with their hubby.
Likewise, Mamono are as a whole bisexual, even if they prefer men. Lesbian sex is not uncommon for both married and unmarried ones, and is one way to turn human women into more Mamono. Though again, it does not compare at all to sex with their hubby.
If that’s the case of futa mamono, then the husband better spread his cheeks wide for her.
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Futa mamono aren't a thing. The only time mamono can be a futa is maybe with a potion, spell, or magical item, however no such potion, spell, or magical item has been confirmed in canon.
The futa hellhound can't hurt you jelly bean. She isn't real.
...
The prison hellhound with the strap on collection is though. Don't lewd the lolis.