You only have enough time to use Furina's skill and transform back ASAP; otherwise, it'll detect you and start filling up its shield meter. C0 Furina is no different from a C2 Furina for this method. You can go beat the Tortoise in a low AR world in coop.
@@kerihtlower its HP first with Furina trick, leave the Sauruon so that the boss detects you and its shield gauge starts filling and then start attacking with your characters from a range to avoid the shield's counterattack.
Boss needs to have its shield up for the 3rd achievement, you can lower the boss HP with Furina trick, but still gotta actually fight near the end. The shield only counterattacks when you attack it from a close distance, so run to the boss, drop Guoba and run away quickly.
