Skarmory

Skarmory can be an alternative prestigier against Rhydon, she won't be weak against any of his moves and deal SE damage. Unless you find a sudowoodo or a pilowswine defending a gym she won't be very useful mon.

I hatched a skarmory from a 10k egg and used it to prestige gyms. It's moves were SW / SA and it did fairly well against a Snorlax.

I've got the same moveset and he's decent for prestiging. Used him against Snorlax yesterday; not bad at all.

I also used my Mantine with B/WP, also hatched from a 10k, to prestige against Flareon and it absolutely crushed him!