Dustin lost his powers in the final battle against Lothor, who stole all of the Ranger powers for himself before being defeated. After graduating from Wind Ninja Academy, Dustin stayed as an instructor.
Dustin has a naive and trusting nature. Marah once conned him into believing that she wanted to turn good, and that she wanted to help the Rangers defeat Lothor. Dustin's instincts about Marah may not have been completely off, as she does seem to have a spark of goodness in her, and possibly a romantic interest in Dustin.