Big Head Mode (Enemies):
After beating Drek, go to the Goodies screen and perform these moves:
Stretch Jump, Flip Back, Flip Back, Flip Back, Stretch Jump, Flip Back, Flip Back,
Flip Back, Stretch Jump, Flip Back, Flip Back, Flip Back and Full Second Crouch.
Big Head Mode (Ratchet):
After beating Drek, go to the Goodies screen and perform these moves:
Flip Back, Flip Back, Flip Back, Full Second Crouch, Stretch Jump and Full Second
Glide.