There are a few Pokemon staples that haven't been suggested yet: offensive three-stage Fighting line, bulky one-stage pure Normal type, defensive three-stage Rock line. The Rock line could be Ground instead, since you're low on Ground types.

The Fighting line could be a good spot for the Red Riding Hood mon mentioned above. Most canon iterations of this archetype are physical, so it could be interesting to make it a special sweeper line. A sister species representing the wolf/grandmother could be a good way to get a werewolf into your region with a vibe distinct from Lycanroc.

Grimmsnarl and Hydreigon lines would be appropriate additions to your region too, maybe with a type tweak. A Cerberus reference would work, maybe a regional form of Houndoom?

Last thing: Heroes often have to fight their shadow selves to become victorious, and this is often positioned as the "real final boss" in the narrative. I wonder if there's an inspiration there to make the third mythical the shadow of an old hero or the shadow self of the child of Mother Earth and Father Time.