No idea what I'm meant to be doing besides just ramming the characters together, seems the winner is always determined by however scores the highest at the start.

I way able to get bouncing on the opponents head with the second character who felt significantly better to control, which felt like I was doing something right but the bar says otherwise.

"Hey Edmund can I copy your homework"
"Sure just don't make it too obvious"

In seriousness, whilst I expected a straight up Isaac rip-off from the thumbnail, I kinda wish it had taken more from Isaac. Isaac has variety and items to keep it interesting, it's more non-linear to add some strategy, here things quickly get repetitive.
Like, I'm not sure why there's randomly generated levels here when non-random would probably be more interesting. Since as far as I can tell you can't perma-die so you're not doing the levels again anyway.

Well polished enough but very unoriginal. I don't think every game needs to be a massive subversion, but a boss that moves slowly back and forth and then drops to try crush you is lackluster when the game's core mechanics are also very familiar.

Character also feels extremely sluggish.

Dying in one hit is also annoying, I never died because it was challenging, just because a hazard was too close to the door and I'd walk right into it.

Really thought this was Pieck from Attack On Titan by the thumbnail.