Ok made it through to the end of the yellow area, also giving me a hard time, but do feel I will be able to beat it. I do suggest however to ... spoiler below ...
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To make the field of view bigger. Quite frequently the boss is off-screen, disabling you from seeing him signalling his attack. After trying dozens of times the off-screen is really causing unnecessary hits, frustratingly enough. Other than that the boss seems reasonably tough, apart from the off-screen bit.