After the first run I realized I can wait at some location or aim to the outer side of the stage to make the middle more manageable. Waiting was usually better since a still target its easier to target. A few ideas that came while playing the game was to have some skills that would move you around or push you, so movement was not as easy to predict at a next loop, also having some area of effect skills that travel through the stage or bounce around (granted I only played with the axe and didn't use any magic so I don't know what you have in store there).
It also seem to me that your clones don't ever despawn, so they get cluster at the bottom, making them easier to kill if you ignore a few and go kill them later. Having the stage have a time limit could solve this, or allowing the clones to leave the stage. Also you could have it so in order to advance to the next loop you have to break open the exit, but on your side of the stage you have to protect your entrance, that way you can't ignore all enemies.
As I said there are lots of way to expand the idea depending on the direction you would want to go. I hope some of this feedback and brainstorming is useful :)