I managed to record both level 9 and 10 clears on my Monday Twitch Stream. Hopefully it provides some insight into how you can approach these two dungeons and the various mechanics they have.
Challenge 10 with Lakshmi
Lakshmi is becoming one of my favourite leaders to use as she provides a healthy mixture of damage control, survivability, and large spike damage. She may not be as well suited for Arena 3, but is more than capable of handling Challenge 10’s.
Challenge 9 with Reincarnated Shiva
My mom and Pancaaake managed to tackle Challenge 9 in coop with their Reincarnated Shiva team. It may have had many heart attacks, but they were successful in the end!
Hopefully these videos provide some inspiration or clarification for Challenge 9 and 10.