Due to the nature of not rerolling until it hits, you can heal yourself back to full health by intentionally not hitting the enemy with it. Exploit or intentional? (it's a bit hard to miss it that much, so I wouldn't be surprised if you let it in to test the players ability at not hitting)
It was interesting, with more skills, or maybe skills that change against each boss, it'd be able to keep refreshing itself on the same system endlessly. Every boss there's a new skillset to master and an enemy moveset to learn, that sounds like the final form for a game in this style.
Fun as it is, and with plenty of potential within. Great project.