So, what are Ghost-types, really?
The Purpose of the Ghost Type:
The primary purpose of Ghost-type is to serve as the undead type of the Pokémon universe and therefore to fill in graveyards and abandoned places for extra spooky flavor, without looking actually decayed stuff. For this reason, an undead type that solely covers grudges and spirits makes much sense. In the later generations due to lack of a dark magic type Ghost-type took over curses and hexes as its element, making the type more associated with dark arts.
Ghost-type also served as another type that would use Psychic-type and Electric-type moves as part of its repertoire, until in the second generation onwards this was flipped upside down, as Psychic-types could not get Dark-type moves due to their status as their antithesis. This restriction no longer exists, and the interaction between the types is now the weakest as part of the demarcation of the types from each other.
The Aesthetic Archetypes of Ghost Types:
Most Ghost-types are either violet, gray or black. Aesthetically they can be divided as such;
Consisting of spirits that haunt items, or live in items, these are the second most dominant form of Ghost-types, often consisting of Ghost-types who have notable secondary types. Like other Ghost-types they are often in Amorphous group, but they tend to have secondary Egg Groups.
The primary form of Ghost-types, these are spirits who are black or dark colored and often mimic part of human form. Ranging from doppelgangers to wailers to greedy imps, these often live in dark areas or somebody else's shadow. They tend to be pure Ghost-type, or allied with another negative type.
The least common form of Ghost-types, these tend to be fairly bright colored Ghost-types that are associated with spirits, but are not phantoms themselves, or if they are phantoms, they have a distinguishable physical form. They often reside in Egg Groups other than Amorphous.
The In-game Archetypes of Ghost Types:
Early game Ghost-type: The least common Ghost-type archetype, these are species encountered in early game with some gimmicks. They tend to be weak either due to low BST or low overall stats, but some can be very strong if they have specific methods to evolve.
Mid-game Ghost-type: The second least common Ghost-type archetype, these are species encountered in early mid-game to mid-game, and they tend to be overspecialize with low BSTs.
Late mid-game Ghost-type: The dominant group, these are the archetypal Ghost-types. As they tend to be close to a mid-game Pokémon, they tend to be weak, and unlike their mid-game counterparts they tend to be not too overspecialized to utilize large movepools.
The Stat Archetypes for Ghost Types:
Sweeper: Traditional sweeper, but in Ghost-types these tend to be slower and more oriented towards to status spam.
Balanced: Species with no specific affiliation, they tend to get by by their types or abilities.
Beatstick: Conventional slow attackers with large offensive stats, these tend to be fairly balanced in other stats.
Annoyer: Conventional annoyer, but since Ghost-types tend to be fairly slow, these tend to have more defense than traditional annoyer.
Dual wall: Conventional walls are a rarity in Ghost-types due to their small HPs, so most Ghost-types are focused on dual walling.
Bulky offense: Conventional bulky offense, but Ghost-types tend to be low HP and slow, so these are more defensive than offensive.
Stat buffer: A variant of balanced, these tend to have some stat tendencies to make stat buffing possible. Calm Mind variants tend to be the most common.