Nice touch with the costumes.
Others may feel different, but from my perspective the Secondo felt a little bass heavy for the subject matter (and I am a person that likes bass!). When I hear this tune I'm thinking video game music from the 80's/90's with plinky 80's computer tone. Perhaps consider lightening the bass for parts of the piece, and bring it back in to heighten intensity in other parts.
Also don't be afraid of intertwining hands and writing the music so you intentionally get in your duet partners space.
Topic: MARIO duet arrangement