Nummskull evolves into Rebone starting at level 28.
Nummskull appears to be a skeleton Yo-kai. He has a round skull with a pink crack on top. His eyes have black scelera with yellow irises with teal-colored pupils. He has a simple black body with pink stripes around his stomach. Nummskull also has lanky arms with far shorter legs.
Yo-kai Watch 3
In Tempura, Nummskull can be found in the Underground Parkway
Coincidentally, both Yo-kai hail from the Tough tribe and their parents hail from different tribes then their children's, with Dazzabel and Gutsy Bones being from the Charming tribe and Shady tribe respectively and both Papa Bolt & Mama Aura being from the Heartful tribe.
Coincidentally, both Nummskull and Frazzel share their respective mothers' ranks (Nummskull and Dazzabel are both Rank E, while Frazzel and Mama Aura are both Rank A).
Nummskull's name is a corrupt spelling of Numbskull which means a foolish or Dumb person.