The bones it possesses were once its mother’s. Its mother’s regrets have become like a vengeful spirit protecting this Pokémon.
– Pokémon Sun Pokédex
While Cubone doesn’t have an Alolan form, Marowak gets one. It becomes Fire/Ghost type (due to its mother’s grudge I guess).
It get an exclusive move, Shadow Bone, which is a Ghost type move, 85 power 100 acc, and has a 20% chance of lowering the target’s Defense by 1 stage.
Stat-wise, it has good Attack and Defense, but is really slow.