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
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