In the Green Grove Boss there seems to be some sort of barrier preventing the spike ball from reaching you on the edges. This is not specific to the DX version and I hope Jon can extend this barrier in some way. It provides an easy strategy for the boss, and I think this should be fixed.
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Also, when the boss gets hit, the water's palette gets messed up.
Nice catch. Funny how this bug wasn't discovered before, as this boss was mostly fough at the center of the level.
Checked this out, and it's present on v0.2. As a note, it happens around the entire border of the playing field, not just the corners. Also, you're not bad at the game, it's just short timing on the hits. No one's judging you for your ability to play the game, you're fine.