Hey, just FYI: the free pack actually contains 11 monsters, not 10. The extra one is the skeleton-lookin' one with orange armor. It's crossed out in the previews on this page and has the filename 10.png (and since filenames start at 00.png, it's actually the eleventh graphic).
HI, Tony! Currently, an Itch purchase only includes downloads. There are no achievements in the Itch build, but the sheet music for the soundtrack is still there!
Thank you for reporting this! I think this may be a Godot issue, but since the final version of the game won't be browser-based, I don't plan to look into this. For now, hopefully you can play via a different browser. 🤞