There is a bug, or a feature, that you can only change bones if the bone is not being healed passively which results in not being able to change bones unless using an auto clicker when you get to very high passive rates... this starts becoming a problem at speeds of less than .5 seconds.
Could have fought the boss at the 40minute mark but decided to max out the cursor damage.... FYI the last upgrade level costs $732.3K... and took around 15 minutes of farming to reach after hitting approximately level 87
You can exploit the boss by going to another screen when your health gets lower and getting the AFK message keeps the boss health low but refills your character, other than that I didn't see any other bugs and had a lot of fun.