I really liked this! \(≧▽≦)/
The map and secrets were really fun to explore. It felt like there was a secret passage everywhere I went!
The originality is a bit low though... I've seen almost all the stuff before in Super Metroid and Silk Song. (^^ ')
Dark Magic draining HP is something that I haven't seen much of in the genre though.
Also, really nice job on the polish and having everything working smoothly. I didn't run into any bugs.
If you could add some background music and more sound effects, I think that would make it even cooler.
Um, and maybe making the enemies more mechanically snake-y would help fit the Python theme more. Right now it's only visually in the theme.
I think that the enemies were quite good to fight, even with just 2 kinds. Juking the vertical-shooting enemy was cool.
Last issue: I couldn't tell if the final boss was taking damage until the moment it died. It would be nice if there was an effect or reaction to it getting hit.
Overall though, my criticisms are just nitpicks. The game was really fun and well executed!
*edit: formatting