Take Surtr as a Support Unit (if you don't have her).
My timings on this run were a bit off, and Cardigan was useless.
For the Challenge Mode, you can use the same strat, but you're gonna need either more healing or more dps for the last wave.
If you can, take better casters, healing defenders, medics and maybe arts guards.
Squad used :
Myrtle, E2 Lv.15, S1M3, P6
Click, E1 Lv.50, Skill 2 Rank 7, P6
Haze, E1 Lv.50, Skill 2 Rank 7, P6
Beagle, E1 Lv.35, Skill Rank 7, P6
Spot, E1 Lv.55, Skill Rank 6, P6
Hibiscus, E1 Lv.55, Skill Rank 7, P6
Ansel, E1 Lv.55, Skill Rank 7, P6
Cardigan, E1 Lv.55, Skill Rank 6, P6
Gravel, E2 Lv.50, Skill 1 Rank 7, P6 (used skill 1 because she is E2, but use skill 2 instead)
Matterhorn, E1 Lv.50, Skill 2 Rank 7, P6
(Support Unit) Surtr, E2 Lv.90, S3M3, P1
Watch video [Arknights] DV-EX-7 Medal - Low-End Squad (w/ Surtr) online, duration hours minute second in high quality that is uploaded to the channel Smashy 25 March 2023. Share the link to the video on social media so that your subscribers and friends will also watch this video. This video clip has been viewed 153 times and liked it 3 visitors.