They're two monsters on that floor and you might have just fought the harder one. Alternatively you didn't have equipment equipped as the starting gear isn't equipped by default in a poor attempt to force people to learn inventory management. Either way not your fault.
My godawful art wasn't something I thought I'd get praised for. Hit detection and sound were the biggest complaints about my last year entry so I obviously put in something but still not great as it still confused some people. I'm putting together a post jam patch and UI scaling was just added to the to do list.