A Morpher class would be an interesting idea. Do you mean be able to Morph into the enemies you are readily fighting against or do you mean akin to Blu, collect obtainable monster DNA to become said monster?

The former is a cool idea but I feel would render potential classes like Beastmasters a moot point because why tame monsters when you can just become the monsters instead?

If it's the latter, that would be an amazing idea. That would mean every enemy you encounter will be crucial to building your skill/spell table. You can create your own unique rotation and chain enemy skills to which youd morph into the DNA of the enemies you've obtained to pull said moves off.