Allowed Units
Overall Strategy
Throughout the entire challenge, each character can only be used TWICE. You want to plan your teams around ending up with the right team for the bosses. So for the normal battles, use characters that you DON'T want to use for the bosses.
You generally want to save "good" teams planned for especially the second 2 bosses, and use "mishmash" teams to clear waves in between.
If you're struggling with having enough characters, you can always level up extra ones to level 70 and not give them talents/artifacts/weapons etc, and just use them as 'dead slots' for the easy rooms and use teams of 3 or even 2 built characters.
First Boss: Terrashroom
Strategy
Fairly squishy boss to be honest. Any well built DPS should be fine to take it down. Consider saving an electro DPS for the terrashroom (ideally NOT clorinde so you can save her for the dancers at the end). But this is your chance to use cyno, keqing, yae, etc very effectively.
Vishaps
Strategy
There's not a particular element that has an advantage, but using a character with great AOE is ideal. Or just saving a good team that can do lots of damage.
The key to the vishaps is killing them both at the same time. So ideally by this point, you have saved a good team that is properly built and synergystic. Perhaps arlecchino, or using one of your clorinde uses for this boss.
Not a Boss but Annoying
Srategy
Recommended to save strong defensive units for this paring, ideally either a very strong shielder or both shielding and healing. Saving thoma for interruption resistance could be a great idea, even Dehya might be quite strong here. Damage isn't the hardest part, it's not dying and staying above 30% HP.
Icewind Suite
Strategy
Ideally you want to save your clorinde for this boss, as she will easily take down the ousia/pneuma shield. But saving a bennett or xiangling team also will work as he can take down the shield very quickly.
Whatever team you pick needs to be able to destroy the ice shield quickly while also doing nice bursty damage during the damage window.
You can also bring the special ousia/pneuma sword 'The Sword of Narzissenkreuz" to more easily take down the shield if someone doesn't really need their weapon.
