Great game! I loved it.
Here are my thoughts.
#1: Overkill damage should be beneficial(50% towards next enemy or something similar)
#2: There should be some more clarity around some things(Ability to hover over keywords especially)
Also, what is the bonus you get from putting multiple of the same sticker on the same thing?
I don't exactly understand Frogs, it seems like there is only 1 instance of them per sticker and it can't create more so if the one dies then that sticker is useless for the rest of that ball?
#3: Track and show damage with each sticker(and base number)
#4: I think mid-run unlockables would be fun(Like Spring could be a good unlockable even) that have prerequisites to reward certain paths.(a Pure dice, one shotting an enemy, etc.)
#5: The ability to increase the speed. The speed is fine early, but as you go later it starts to feel really slow. So I would just add a 2x and 4x option.
#6: It could be fun to have a rare or expensive ability to skip placing a sticker, reroll your sticker options or replace an already existing sticker.