pretty much what happens after the boss fight.
Shinkyoku learned Reignite Gloomiere has a strong attack stat, but it comes from his weapon: the lantern. With every attack, the lantern's light dims a bit until the light completely dissapates. This will lock Gloomiere in a scared state; preventing him from attacking. the only way to undo this is to use certain skills or items such as Reignite or wisp in a cup on Gloomiere. doing so will reignite the Lantern and return Gloomiere's emotion to normal.