Super fun concept! I liked trying to figure out the different combinations in order to be successful with each boss... At first. I'm not sure if it was a combination of multiple losses or just too many fights overall, but the trial-and-error got old over fight 4 or so, even with the Scanner or the tips. Maybe consider building the town out a little more (and improving on the mapping a bit) to include a Pub or something where other contestants have gathered and are talking about the next available boss. Have some of them offer vague tips or ideas about what kind of build might work, but also have some mention things that are misleading. Then the construction of your party is actually more of a puzzle than trial and error and more rewarding for the player who bothers to talk to the NPCs.
The battle system is really unique and and I think the idea of this game is definitely something cool, it just needs some more elements fleshed out a bit more.