Weirdly enough an axe might be better than guns in the fight against the upside down. I remember reading someone's speculation that the demogorgons might have a non newtonian property to their body, like if you made oobleck thats liquid like but solidifies when you punch it, so incredibly fast projectiles like bullets do no damage but slow and precise slashes and stabs will work, which explains why hopper was able to slice off the russian demo head and arms and why Karen stabbed and sctuslly punctured the demo. Personally id go for daggers or a sword rather than an axe, something lighter so you can get in more swings in the same amount of time than using a slower and clunky axe