>>27727920>Can anyone explain why Cubone in Alola suddenly become Ghost types? Do they die when they undergo their metamorphosis similar to Froslass?Well the reveal says the following:
"There are many Grass-type Pokémon—Marowak’s natural enemies—in the Alola region. This makes Alola a harsh environment for Cubone and Marowak. As a result, they live in close union with their partners. It’s said that their great care for their partners allowed them to gain something like a sixth sense and resulted in their changed form."
Instead of abandoning their young, Alolan Marowak commit significantly more time, resources and patience into raising their cubone children. So much so that Alolan Marowak's have a much more personal bond with the cubone/marowak bones they use to defend themselves. This personal relationship is most likely infused into the bones and translates into that "sixth sense" allowing the type change.
Now, This part is head-canon, but I've always believed that Marowaks lay their eggs in the same spot they go to die(Think a Marowak/Cubone Graveyard): The cubone hatch and use the bones of their ancestors/relatives to defend themselves, etc.. Besides this act though the species is entirely asocial with Marowaks being particularly aggressive.
So, yeah.
+Bonus Fact+
"The Marowak in the Alola region take bones and light both ends on fire by rubbing them against their foreheads."
The Black Marking on an Alolan Marowak is a rough-patch of exposed hide the Marowak uses to light it's bones.