Throughout the Pokémon series and games, up until Generation VIII, there are a total of 56 Ghost-type Pokémon, with some being pure Ghost-type, and others having Ghost as a secondary type. With the ghost-type being considered one the best types through the Pokémon franchise, getting a spot there is a big deal for Pokémon.
Nevertheless, some of these Pokémon manage to stand out as they simply seem not to fit the Ghost-type at all, due to not being scary, spooky, or resembling ghosts at all. On top of that, these Pokémon would make far more sense if they belonged to a different type.
Palossand
Palossand is a Generation VII ghost and ground-type Pokémon and although its previous form, Sandyghast, resembles a ghost both in appearance and in name, Palossand is far from that.
As it looks like a sandcastle, the ground type seems perfectly reasonable, but it should be combined with either a rock type (due to being in a rocky beach) or even a water type, due to being built by sand next to the sea.
Decidueye
Despite being one of the coolest Ghost-type Pokémon in the series, Decidueye looks nothing like a ghost. With its appearance resembling a tall grassy owl, Dedicudeye is nothing close to grass and ghost-type Pokémon.
As an owl, the first obvious choice would be the flying type, while the second would be the dark type, due to owls being nighttime creatures. Even the grass type could be maintained due to its grassy textures and colors, but definitely not the ghost type.
Oricorio (Sensu Type)
One of the four forms of Oricorio, the sensu-type one, has the flying and ghost type. As its appearance is that of a bird, the flying type makes perfect sense. Nevertheless, it bears no ghost elements, neither in name nor appearance.
The only thing that could seem relevant to a ghost-type would be its dark blue and purple color palette but that can be a bit too far-fetched. Perhaps it would be better explained as a dark-type.
Dhelmise
Dhelmise, a ghost and grass type Pokémon bears a creepy appearance and could be interpreted as a ghost-type initially, but there are other types that are far more fitting to it based on its appearance it is an anchor full of seaweed. Due to the seaweed, its grass type is spot on, but only if combined with a water type.
After all, it is an anchor, and seaweed is only found underwater. On top of that, it is described by the wiki as a sea anchor Pokémon, which makes the water type even more fitting.
Frillish
Frillish is a generation V water and ghost-type Pokémon whose appearance resembles a jellyfish with its evolution being considered one of the most underrated ghost-type Pokémon. The ghost type would make sense if it was to some extent justified in the official wiki.
Nevertheless, it is presented as a water-type monster that lives deep below the sea and uses its poisonous spikes as a way to catch its prey. Thus, it is more of a water and poison type, than a ghost as it bears no ghostly elements at all.
Blacephalon
Blacephalon, a Generation VII fire and ghost-type Pokémon that resembles more a famous painting with a weird mix of colors than a Pokémon doesn't seem to rightly belong to any type.
With its appearance being more confusing than helpful and it being able to learn moves of multiple different types, perhaps the best guess would be to have it as a psychic type combined with its already existing fire type since it is described as the firework Pokémon.
Dreepy
Although its last evolution might resemble a ghost-type more accurately, Dreepy is far from that. As a dragon and ghost type that looks more like an amphibian or a serpent than anything else, it would be more fitting to assign it to the water, grass, or even bug type.
The same seems to apply to its second evolution, Dracloak which seems more like a water than a ghost type.
Doublade
A Pokémon whose appearance resembles two swords crossing and isn't a fighting type definitely makes no sense. As a Generation V Pokémon with steel and ghost-type, Doublade doesn't have enough elements to justify its ghost-type.
On the contrary, its appearance, as well as the fact that it can learn fighting moves by leveling up and by TMs, make it a great fit for either a pure fighting type or even a steel and fighting.
Shadow Rider Calyrex
Calyrex, the Psychic-type King Pokémon introduced in Generation VIII can be transformed into Shadow Rider Calyrex and become a psychic and ghost type. With its appearance resembling a psychic Pokémon riding a dark horse, the horse would be more fitting to provide the Pokémon with the dark type instead of a ghost type.
Also, since Calyrex is known as the King of bountiful harvests, perhaps it should combine its Psychic-type with a grass-type instead.
Marowak (Alola Form)
Marowak, in its Alolan form, transforms from a pure ground-type to a fire and ghost Pokémon. Although it makes some sense due to its spooky vibe, stripping it completely of its ground type can be a bit too much.
Perhaps maintaining its ground-type and having it combined with a fire-type as its' weapon appears to be on fire would be more fitting.