This review will not be as long as the title would suggest.
Mob Psycho 100 is seeing the release of some OVA's, this first one taking place after the end of the second season. That being said,this is the length of a normal episode so this review is essentially me trying my hand at reviewing a single episode rather than a full show, so let's see how this goes! Spoilers if you haven't finished season two of Mob Psycho.
Reigen decides he is going to take a case of a haunting at a hot spring, guests are saying they are being taken to another world while there and leaving exhausted. All of your main characters are here, in addition to Reigen's newest assistant, Serizawa. At this point, it should be noted that only three of these characters are actually important to this episode: Reigen, Serizawa, and Mob. The rest of them kind of feel like a dead weight that doesn't really need to be there. It seems like they just felt obligated to make it a big group activity for the OVA, but so little time is given to anyone else it feels a bit pointless.
And to be honest, Mob is really only their as the cleanup for the episodes foes, the main story revolves around Reigen getting trapped in this alternate world and trying to find his way out. As far as psychic enemies are concerned, this actually isn't that hard for atypical psychic to detect. Anyone familiar with the show knows Reigen isn't actually psychic, but his assistant who is trapped with him is socially inept and doesn't want to step on his bosses toes and upset him.
No one on the outside is aware of why Reigen is sleeping so much,and the episode basically acts as a pure comedy as you watch Reigen slowly start to lose his mind attempting to escape the world he is trapped in and Serizawa just comes and goes as he pleases. I'm kind of glad this is only a twenty-minute OVA, because any longer the joke would probably get old after a while.
The show cuts back and forth between Mob and friends in reality and back to Reigen struggling to realize the secret of this world and escape, while Serizawa comes and goes looking perfectly normal and reasonable. This, of course, leads Reigen to thinking Serizawa is the one who has gone crazy.
This is honestly just a solid filler episode of Mob Psycho. You don't learn anything about characters you didn't already know, but the jokes are there and the show gets a laugh throughout it's run. If you come across it definitely watch it, though it's only really worth watching as a quick laugh, and isn't likely something you are ever going to come back to.
