I was having one of my best runs ever with eyes, and I proceeded to fight the final enemy of the level (A level 4 fly) with full hp, I broke 1 of his dice and burnt the other (don't know if this had anything to do with it), then the fly used his third card (didn't get to read what it was) and basically used it like 20 times due to an error and instant killed me.

This line of code, apparently: 
myeq.canuse = 0;

Edit: The card was one that said "Attempts to Poison", and there's no need for status effects in order for him to just end you in one hit.

Edit2: For more in-depth stuff check 'Softlock (Explofreak)'

I got a video of this happening! I'm uncertain if it'd add anything to it, but I find it amusing since the more I think about what's happening, the less it makes sense.

We already got the source of the error, it has to do with some stuff that doesn't quite work on the cvs

I may just fix it on my Character Rebalance mod soon enough, already got it fixed on my build so it shouldn't take long.

Check "Softlock (Explofreak)" for more info on the error.