In “Pokemon GO,” the Pokémon that wears the skull of its dead mother on its head is Cubone.
Cubone’s skull is identified in Pokédex entries as the skull of its deceased mother, Marowak. The bone it carries is also associated with Marowak, giving Cubone one of the most recognizable and melancholy origin stories in the Pokémon series.
Cubone is a Ground-type Pokémon introduced in Generation I. It evolves into Marowak at level 28, meaning the species eventually becomes the same Pokémon whose skull Cubone is said to wear. In Pokémon Sun and Moon, an Alolan form of Marowak was introduced with a Fire/Ghost typing and a distinctive spirit-flame fighting style.
A common mix-up involves Kangaskhan: a long-running fan theory proposes that Kangaskhan may somehow be connected to Cubone’s mother, but this is not official canon. The games’ direct explanation is that Cubone wears its dead mother Marowak’s skull.