After reinstalling (which I did to see if it would fix some of the audio troubles), the level 2 attack still fires off with a quick tap of shift+enter, but only if I have at least 2 fireflies. Still working correctly in survival.
hm I can't recreate it on my end but I'll have to rework the system anyways. Hopefully it can be fixed then. Uploaded another version with different sounds, hopefully that will be less buggy.