Great job! I really like your take on the power mechanic.
I couldn't reach the 5 flags because when I died I had to start all over again and the game is not that easy (which is fine). So my only advice would be to save progress on the completed islands, it would also benefit a lot to the game loop, also maybe the upgrade could've come a bit sooner than 5 flags. But overall amazing :D
Also great job on the destroy animation and sfx