As part of its ongoing efforts to promote every single Pokémon out there, The Pokémon Company has shared special content dedicated to Marowak:
Did you know? This Pokémon overcame its sorrow to evolve a sturdy new body. Marowak faces its opponents bravely, using a bone as a weapon. When this Pokémon evolved, the skull of its mother fused to it. Marowak’s temperament also turned vicious at the same time.
Source: The Pokémon Company