Here's an AoE-heavy auto template for Master Asura's Trial, newly released today with Annelie's spiral. This uses proper units and dragons, as it's not really possible to build a non-RNG budget unit team for this given the lack of AoE in the lower rarity units pool for Shadow. As with other DPS check fights, this uses a ranged/lance lead with long lock-on range for best DPS uptime. In this case, S!Verica herself is the lead and also contributes to DPS via a strong dragon in either R!Nidhogg or Bahamut (or Ramiel if you really need to stretch it).
The mechanics of this fight are very straightforward so I'll keep it quick:
There is a weak-point check (1-2 times)
There are many AoE checks (sphere adds, many times)
To deal with these in Auto, you do the same as usual for fights with these mechanics:
Ranged or lance lead unit for long lock-on range
Remove Agito Skill on backline AI (use Off-element weapons)
Use Skill Haste to increase frequency of skill usage (ie. Bow Psalm + Sword Psalm)
Bring AoE units (Gala Cleo and/or Alberius are key)
Unit choices & possible replacements:
Healer lead: Summer Verica (get her from the Fall 2021 Dream Ticket if you need to)
AoE DPS: AoE units - Gala Cleo and Alberius are excellent
Secondary DPS: Good AI/utility units - Summer Patia, Gala Zethia, H!Sylas, many units can work here.
Skill shares: Very flexible. I used Cassandra for +30% Max HP and a bit of damage, plus Mym for Dgauge + damage
Lead dragon: R!Nidhogg or Bahamut work best due to their great dragon forms. R!Nidhogg gives you more time in dragon but slower clear times, so you can try Bahamut if you have him too. Ramiel would be the budget option here.
AI dragons: Str dragon on S!Patia, others can use your other premium dragons. 5UB Chthonius is a great filler dragon for Gala Cleo as she doesn't have much personal DPS anyway.