The game doesn't tell you how to get a Ghast Tear. It should mention needing to fight an enemy Drifloon. Consider having Shedinja drop them.

It's possible the incense quest (w/ skull, ghast tear) isn't consuming all the ingredients.

With tear that wasn't being awarded at the start, there shouldn't BE a need to explain where tears come from, although an explanation was added to the farming section.

Incense quest now consumes ingredients.