>>90422971>Marco still has a pair of scissors, right?Most likely, Moon had her own pair which likely made the portal her and Star eventually used to go home. That being said, Star had been shown possessing them in recent episodes. I imagine we'll get confirmation if he still has them in season 3's first episode.
>Do we know what actually happened to Glossarick?Nope, he's awol as of the finale. Ludo mentions him disappearing when the high magic commission is grilling him for info.
>Do we know what the Underworld's diplomatic position is towards Mewni?As
>>90423031 said, things seem to be rather positive between the two, based on Star's input in the recent Star vs. book, which, I would imagine, shares the same canonical liberties as the comics do, that being canon with the show's universe.