this is a pretty good game, but after 5 minutes either a: optimize as the game gets laggy but not to the point of unplayable, just slow and really annoying, or b: either hide coin drops, have some sort of super magnet upgrade that you can get (or make the robot collector better and only appear after boss defeat) as hes completly useless rn collecting only one coin per time, there were just too many coins that i couldnt collect, c: an cool way to challenge yourself is so bosses can just be infinitely resummoned with the same eniemy scaling (im assuming that its some sort of multiplier) but not give boss chest / reward, mabey super magnet that vaccums up every coin on map, or just give an increased amount of coins d: increase eniemy scaling either the decreased acceleration bullet upgrade is too strong, or the eniemys dont scale hard enough i stayed till 14 minutes till i quit cuz it was too slow, but the enimeys was 0 challenge (most important to fix would be magnet and optimization) was one shotting massive groups with ease btw 
Thank you so much for the detailed feedback!
The optimization problem is already solved on the pc version, its just having problems on the browser, might implementing the coin magnet or any other coin picking mechanic seems like a perfect ideia! Thank you!
The full version will has multiple levels, and the option to replay like you are saying (and still giving items, because the difficulty is going to scale faster and if you choose to stay behind you will be rewarded but the game will be harder).
Thank you so much for playing so much and leaving feeback, can I count you in a playtester when I launch the playtest? :)