Except the bosses who is easy to be defeated like Remy and Wulie,I think Mushna should fight first,because you can take umbrellashroom,which could help you pass faster and make the boss fight easier.Or you can fight with Momo first,you can get puppet which would help you attack enemies,like Lip said.But I like to move more convenient,so I'm used to fight with Mushna first,just according to your choice,both ok.If you don't have special requirements, you can do it according to your preference.