Walkthrough
After returning to the Dojo with the Max Mushrooms, Mustard and Honey will proceed to making the Max Soup. Just as they begin to make the soup, Klara/Avery will arrive with more Max Mushrooms and Mustard and Honey will decide to be friendly and use their Max Mushrooms instead of yours (allowing you to make a separate batch of Max Soup later on). After dining on the Max Soup, Mustard will request to see Klara/Avery and your trainer. It is then that Mustard will announce the third and final Trial to obtain the secret armor, and it is nothing more than a battle between the two of you. When ready, head to the back of the dojo (where Dynamaxing can take place in battle) and face Klara/Avery in one final battle. After defeating them, Mustard will give you the secret armor of the dojo, which actually will turn out to be the Legendary Baby Pokemon Kubfu!
Pokemon Trainer Klara (Sword): Level 23/65 Skorupi, Level 24/66 Galarian Weezing, Level 24/66 Whirlipede, Level 25/67 Galarian Slowbro.
Pokemon Trainer Avery (Shield): Level 23/65 Galarian Ponyta, Level 24/66 Swoobat, Level 24/66 Kadabra, Level 25/67 Galarian Slowbro.
Now that you know about Mustard's Third Trial, Click Here to learn about the final battle against Dojo Master Mustard!