Season 2 of Mob Psycho 100 was announced at the end of the OVA.
Mob Psycho 100 Reigen: Shirarezaru Kiseki no Reinouryokusha
Mob Psycho 100: Reigen – The Miracle Psychic that Nobody Knows
モブサイコ100 REIGEN ～知られざる奇跡の霊能力者～
For those asking about the song:
The artist is called Kenji Kawai (川 井 憲 次), and the song is called “A first love’s feelings!” (初恋の気持ち!)
It can be found on the Japanese iTunes: https://itunes.apple.com/jp/album/モブサイコ100-original-soundtrack-音楽-川井憲次/1168949474 as 25 初恋の気持ち!
MAG.MOE - The MAG, The MOE.