I think this is actually a personification/cosplay of Cubone, not Marowack. The "skull" has no lower jaw and the bone being held tapers whereas Marowaks doesn't
You guys need to go check Cubone and Marowak again. Cubone has larger eyeholes and a more rounded front, Marowak has a tapered 'sharper' front and eyes similar to this one. The bone tapering could be how its being held as a few of the official sprites seem to 'taper' from the front.
Plus the artist has stated its a Marowak. Changing it back