Not a lot is known about this deity, except that he is a he, and that his name, Maponos, means “Great Son.” There isn’t much known about Maponos except that he is a god that is Celtic and also a Roman god.
He was worshipped by the Parisii, who lived in Gaul (modern day France) on the banks of the Seine, which is the land that France now sits on. During rhat time period the people were Celtic and Roman, as the Romans later conquered the Gaul.
Maponos is a god of the hunt, and youth. He is also compared to Apollo (Apollo Maponos), who has a twin Artemis and they were unable to be born on any land due to Hera preventing Leto to be able to give birth on land, so she went to the island Delos to give birth to the twins. Maponos is depicted as having a lyre and being a god of music as well. He was worshipped by some of the Roman army.
He is compared to Aengus, an Irish god of love, who was born in a day to his father Dagda, bending time of nine months to fit under the same day of his conception to hide his infidelity with Boand, the river goddess of the Boyne, because she was married to Elcmar.
He’s also compared to Mabon ap Madron who is in Arthurian legend. He’s the son of Madron, and they are also a son and mother pair, similar to how both Apollo and Aengus had unique births, however Mabon was taken from his mother when he was three days old instead of having a different birth.
Unfortunately, there isn’t any actual known myth (by what I have been able to find) with Maponos in it. However, it my own personal gnosis that Maponos is very connected to nature, in how he is a god of the hunt. So he could also be compared to a few other gods, what immediately comes to mind is Ullr, then Frey do to how Aengus was love sick after having dreams of Caer, similar to how Frey was love sick for Gerda after seeing her on Odin’s high seat. Then, I also see a connection with Cernunnos and Maponos, even though Maponos doesn’t have horns, although he may be a horny god.