Lots of great feedback, thank you!
There is absolutely a lot more to the game than just beating the current 10k health boss. A lot of other ideas are currently in the works. The numbers will be going all the way up to quadrillions.
Very good point about regen hearts. They're the least fleshed out mechanic at the moment.
Being able to upgrade runes with gold is an interesting idea. I didn't think of that! Noted it down.
I'll be following along closely to see where this game ends up going! Definitely interested in seeing how a quadrillion health boss comes into the loop and how the mechanics evolve as you get more ideas and refine some of the kinks but already it's super polished for an alpha which makes me pretty hype for the full release however long down the line! Something tells me it'll be a fun experience!