The biggest challenge in this game would be, to find the collectable items. There should be some kind of hint to guide the player to the collectable. Avoiding the red circles weren't really a challenge for me.
On the technical side, the gameplay on HTML version showed signs of incremental stutter over time, and the EXE version is missing the PCK file.
However, this was a good simple collect and avoid game. Tail effects were nice, and the ending was funny.