TLDR at the bottom.

Not sure if this is well known, or I am a discoverer of great knowledge, but I found an amazing hidden ability to the Notched Axe. I was on the second loop on It's All Mine II.  A stoner had unfortunately broken through my line of deserters, and this was early enough in the level that my back line wouldn't be enough to destroy it. I don't know how this clicked in my brain (maybe due to stoners having obstacle-like attributes?) but in a moment of desperation, I grabbed the Notched Axe, and, sure enough, it took away the remaining health of the stoner!

Haven't been able to test on other enemies, but it doesn't work on all enemies, since I tried a gaper.  I'm guessing it works on hardies, and possibly the helmets of hardheads, the former of which could be immensely helpful. This would make this item one of the better ones on Mines, especially in later loops.

TLDR: Notched axe can destroy Stoners, probably hardies, and potentially hardhead helms. Item good on mines.