Was wondering what use the money was until I ran into the first upgrade, and after that I started collecting money, for when I'd need it... but it seems to disappear at random intervals. After a certain amount? After a certain level? After a certain amount of levels? is this intentional...? Wish there was some form of Continue, too, when you die. Maybe one you could upgrade for. Buy yourself a checkpoint or a restart with a hundred coins, for example. Some kind of limited safety net at least. I like simplicity, so this is the right kind of dungeon for me, though just hitting the wrong room it's all too easy to loose all your progress in just one swoop.
Otherwise good game! Simple but with appreciated variation with enemies, an almost comical whirl transition between levels, smooth controls... just need to polish the reward and grind mechanics a bit IMO. Also the spikes: maybe not visible enough...
-cd-