Great! The polish shows, and the "loot" for motivation is a great touch.
A few minor suggestions and questions:
In Ulgrax, the interact keybind doesn't pick up the dead adds (if it should?).
In "Silken Food Court", perhaps detect if the player is just waiting in the web area instead of running into the central cocoon itself. Dunno if you want to have the teammate do it, or clarify messages / have a specific fail message.
In "Juicebound Horror", perhaps have the other group (barely) fail to finish off one of the adds. (...or if that isn't the reason the groups are getting together, whatever the reason is?)
For pausing and going back from menus, Esc gets overridden by Chrome for exiting full screen first, so you might want to add and show a different key for those.
Thanks a ton for this!