It's a nice tight little metroidvania (but not a minivania) with a retro style halfway between NES and Game Boy Color, I bought it during the Steam sales, played a few hours and quite enjoyed it.

You play as a little rat dude bashing (hence the title) cryptids and other monsters with a metal bat and later other weapons; there are gates that can be passed by defeating a certain number of enemies, but they can be easily skipped (indeed there's an achievement for beating <10 enemies in the whole game) if you manage to buy early movement items like wall climb, backflip, double jump etc.

It's in fact really open-ended and I often found myself in areas where I wasn't supposed to be yet or that could be completed more easily by buying certain items (the one that nullifies fall damage is a must), or beaten bosses and after some time finding NPC that told me where they were and how to fight them; but that's part of the MV charm for you.

My only problem is that the NES style is imitated so well that the controls feel a bit clunky and slippery (double-tapping the direction to run is kind of annoying), but you get used to it, and it's part of the whole theme: to beat cryptids you first have to shine the light of your flashlight on them, so it kind of makes sense that you can't move as fluidly when you are holding it. For the rest however it's quite well-made, including the chiptune music that feels authentic for the most part.

As a kid I was obsessed with monsters and other weird shit, so I believe that, if this were an actual NES game, I would have been all over it! But it's still quite valid if you enjoy this type of retro indie titles.