I think the last mon could be Stoutland because it works really well on this team, basically because it has a Sand setter and the team lacks a powerful physical attacker, , I'm pretty sure that his last is Stoutland. Stoutland helps clefable to find setup opportunities, makes the matchup of the team much better against stall.
and the team is lacking a solid wallbreaker since Mega Aerodactyl is using a very specific set.