The Inner Warrior is a song from "The Gi" that Gumball and Darwin get "inspiration" from. They do air guitar and karate moves all throughout it. Richard apparently knows the song, as he joins in later; stating that it is a great track. It was sung by Willie Dowling.
Every time I look in the mirror, all I see..is the inner warrior staring back at me!
You hit hard with your best shot, give it everything you've got; Warrior, be the warrior!
Bring 'em on, let 'em come, they will never keep me down; Come on Warrior! Be the Warrior!
'Cause you're the best that you can be.
Yeaaaa aaeeeaa aaa yeaaa