This OVA of Mob Psycho 100 is basically just episode 14 of season two. The story is a direct continuation and appears to happen only days after where the second season left off. It follows the standard format where Reigen accepts a job and then has Mob help him exorcise the spirits. This time the story takes place at a hot spring and they brought some more people along. The main focus of the story in this episode seems to be Mob and friends just having a good time. The Main characters are Reigen, Mob, Mob's little brother, Hanazawa and Serizawa and aside from Reigenthey mostly just have a fun trip.

The animation sound and voice acting are all comparable to the second season.

Overall this is an extra episode and there's no real reason not to watch it if you enjoyed the anime so far.