i got the other three i cant find the fourth one, help please

Stuck trying to find this one. HELP!

just asking...

If you go back to visit your mom after acquiring the beaver form and you change to slime form and step into the water where it's okay for a slime to move, and open the forms menu by pressing shift, the game will crash with the error "Typerror cannot read property of 'traits' undefined"....