Ok, looks like I forgot to set the size for the browser player, but it also looks like the file didn't zip properly and is missing files, hence the issues with the slimes. Course, you're not supposed to be able to see them in the first place since they're just placeholders, so there's something else for me to fix, lol. I'll reupload later with something that will hopefully work
EDIT - Found the issue, when rpg maker deployed it it decided that the images I clearly called were not ACTUALLY being used, so it didn't include them with the deployment. Hence those errors. Now the issue is, it refuses to include said images if I try to exclude unused images, so I need to include them all, but then it's too big to play in browser. I'll upload a zip you can download for now while I cut through what I can get rid of.