Found a bug while watching MegaHarv stream. During the first Sigma Fight (as in, the fight immediately following the dogs), it is somehow possible for X to become completely immune to damage for a while. Not 100% certain what caused it, or what made it stop working, but it was clear it wasn't intended (there was no item he used, and there was no indicator it should be happening etc). This was version 1.00.4
I haven't played that version yet, I've only played 1.00.2 and it never happened to me on there, so I'm not sure how to go about reproducing it. If you want to see it you can find his channel on youtube (@MegaHarv), should be pretty easy to scrub for since it's near the end of the game, the VOD should still be there (it was at the time of writing and he generally doesn't remove them himself).