If Lin attacks with Flash cannon on a circuit field there's a way to repel this:
1. Have a Mawile hold a Babiri berry, that should weaken the damage by Flash Cannon.
2.Have a figting type, since Hydreigon is weak to that (right?).
3.Have a Mamoswine with focus stash.
4.Have an pokemon that knows dazzling gleam, plus great speed or with Speed Claw.
5.Any fairy type hold a focus stash or a baribi berry and shall do fine.
Of course those are hypothetical ways, not saying it is the actual way, but hey , might be usefull