This Misty Valley guide will recommend formations that don't include Celestial, Hypogean, and Dimensional heroes unless necessary or a Silver Challenge requirement. I hope it will help you complete all 60 challenges and unlock all 60 reward chests.
If you need more formation recommendations for a particular stage, feel free to leave a comment with your available heroes and I will try to help you.
Also, check my AFK Arena hero tier list and be on standby for more AFK Arena codes.
Notes
In cases where there was a 4-faction requirement, I tried to use 5 heroes of the same faction. Just replace one with your main carry.
When the enemy formation contains Kren try to kill him fast as he hits very hard.
For stages where one hero needs to kill 3 or 4 characters, I recommend you give them the Wrizz and Soren treatment with a 1+4 setup. Let Saurus make the killing and surround him with four support heroes tanky enough not to go down fast and let Saurus be overwhelmed. If your Saurus is SI +30, then these two stages should be a piece of cake.
Note: This is the stage 1-10 guide for September's Misty Valley event.
| Silver Challenge Requirement | Recommended Formation | Gold Challenge Requirement | Recommended Formation |
|---|---|---|---|
| Stage 1. 4 Lightbearers | 
 
| Achieve victory without any heroes dying. | Same as silver. |
| Stage 2. 4 Maulers | 
| Defeat an enemy hero within 10s. | Same as silver. |
| Stage 3. 4 Wilders | 
| Ult <= 4 times. | Same as silver. (0 Ults) |
| Stage 4. 4 Graveborns | 
| Team contains Anoki & Skriath. |
(My Anoki is LVL 1) |
| Stage 5. 4 Celepogean/ Dimensional |  
| All heroes are in the same class. | Same as silver. |
| Stage 6. 4 Lightbearers |
| No Support or Mage heroes. | Same as silver. |
| Stage 7. 4 Maulers |  
| Three tanks in the back row. | Same as silver. (Tough: Granit & Anoki are LVL 1). |
| Stage 8. 4 Wilders |
| Team contains Scarlet & Isabella. |
(Isabella is lvl 1) |
| Stage 9. 4 Graveborns |
| Defeat at least four non-summoned enemies with the same hero. | Same as silver. (Grezhul does it) |
| Stage 10. 4 Celepogean/ Dimensional |
 
| Achieve victory with five different faction heroes. |
|
| Stage 11. 4 Lightbearers |
| Win in 20s. | Same as silver. |
| Stage 12. 4 Maulers |
| Victorious team contains Saurus & Eironn. | 
|
| Stage 13. 4 Wilders |
| All heroes belong to the same class | Same as Silver |
| Stage 14. 4 Graveborns | 
| Frontline heroes must be mages. | Same as silver. (Shemira is level 1) |
| Stage 15. 4 Celestial /Hypogean/ Dimensional |
| Don't trigger Ultimate abilities more than three times in battle. | Same as silver. (0 Ults) |
| Stage 16. 4 Lightbearers |
| Team contains Astar and Talene. | 
(Talene and Astar are level 1) |
| Stage 17. 4 Maulers |
| Defeat >= three enemy heroes with the same hero. | Same as silver. |
| Stage 18. 4 Wilders | 
| Five different factions. |
|
| Stage 19. 4 Graveborns |
| Victory without Tanks and Warriors. | Same as silver. |
| Stage 20. 4 Celestial /Hypogean/ Dimensional |
| Victory without any heroes dying. | Same as silver. |