Amazon has put up the product page for the third volume of the Mob Psycho 100 manga, revealing the cover, release date as well as several other details. If you are interested, you can preorder the book (which is being published by Dark Horse Manga with an ISBN-10 of 1506709893 as well as an ISBN-13 of 978-1506709895) with this link from the online retailer; furthermore, you can also take a look at the front cover design with the image located just below this paragraph.
You can also take a look at Amazon’s product description for Mob Psycho 100 Manga Volume 3 below:
In a showdown with Black Vinegar Middle School’s shadow gang leader, Teru, Mob sticks to his policy of nonviolence and refrains from using his powers–and gets knocked out! The fight seems over for Mob…but something then awakens in Mob, beyond the confines of his conscious mind! And in the aftermath, a new story develops with Ritsu, Mob’s conflicted younger brother who enjoys the social success Mob desires…yet still longs for what Mob has that Ritsu lacks–psychic power!
Mob Psycho 100 Manga Volume 3 will be released on July 9, 2019, in the North American region. So, if you are a fan of the anime, then you might want to check out the manga series.