Potential Overflow Bug in Phobos nether boss-fight

So, I was getting straight rolled over in the Phobos boss fight, being pretty unprepared for the cool mirror passive thing, but after all of my creatures except for one (Pegasus/Nex Seraph w/Lunar Ending artifact) were killed, this Pegasus hung on for many more turns before I noticed that, every time I attacked with it and began proccing the Phobos’ barrage of mirror attacks, my Pegasus was gaining maximum health. It’s gone from ~4k to 51k at this point.

Here’s a few turns later. The Max HP bounces around constantly while I’m taking hits, but it always ends with the pegasus at full health and at much higher Max HP than it started with.

And it resolved by my pegasus suddenly dying at around 95k max HP (sorry, no picture, it took me off guard). Not sure what caused it, I didn’t have anything in my kit that could increase max HP at all.