Introduced in the Red & Blue generation one games, the Gastly line was the only Ghost-type Pokemon for an entire generation until Misdreavus was brought in with the Johto region. Even though there are many more Ghost-types in the series now than there were in the beginning, the Gastly line is unique in being the only Ghost/Poison-types in the series.
The first evolution of this line, Haunter, may get somewhat overshadowed by its final form, Gengar, in terms of both design and usability, but there's a lot to love about this Pokemon and it shouldn't be overlooked just because it needs to be traded to evolve. Due to its status of being the awkward middle evolution, there are also many aspects of this Pokemon that fly under the radar and go unseen by the players as a result.
10 Its Weight
As a giant ball of floating gas, it should be no surprise that Haunter doesn't weigh all that much. Coming in at a tiny 0.1kgs, it is part of the group of the lightest Pokemon in the series, tied with Gastly, Cosmoem, Flabebe, and Kartarna. Comparing this to Gengar, which comes in at a whopping 40kgs heavier, it's somewhat of a mystery as to what is so different about Gengar that makes it so much heavier than its predecessor.
9 Its Size
Unless players have seen Haunter as shown in the Let's Go games, it's easy to be mistaken concerning just how large Haunter is compared to other Pokemon. Floating at a respectable 5.3 feet tall, this makes it the same size as the likes of Blastoise, Volcarona, and Metagross. This height apparently doesn't account for the space between its body and the ground, since it is large enough to ride on in the Let's Go games and is even larger than Gengar, which is only 4.11 feet tall.
8 It Has A Minimalist Shiny Form
There are several Pokemon in the series that take on a drastically different color palette when they are in their shiny form, though Haunter doesn't fall into this category. Unless its mouth is open and displaying its very impressive tongue, it's almost impossible to know whether or not a Haunter is shiny.
While Gengar also suffers from its shiny form being almost identical to its standard coloration, Haunter's shiny form only affects its tongue for some reason, changing it from pink to blue while the rest of its body remains unchanged.
7 Its Learnable TMs Are Mostly Physical Moves
The Gastly line has a fairly well-rounded movepool despite the fact that it's generally limited to Ghost, Poison, and Psychic-type attacks. While it does have access to other types of attacks, these are all, unfortunately, pretty much limited to physical moves such as the elemental punches. Haunter and Gengar do have access to some powerful special attacks for coverage, such as Dazzling Gleam and Thunderbolt, but its movepool has the potential to be so much more diverse if it had the Attack stat to back it up.
6 Its Special Attack Is Comparable With Some Legendaries
The fact that the Gastly line is focused on its Special Attack stat may mean that it has some shortcomings when it comes to its movepool, but this also means that it is able to compete with the best of the best when it comes to its special attacks. With a base stat of 115, Haunter has the same Special Attack as Raikou and an even higher stat than Solgaleo, Ho-Oh, and Latias. While not as impressive as Gengar's 130 Special Attack, 115 is more than enough to stand on its own merits and means that players don't need to necessarily evolve it to get the most out of it.
5 It Can Lick People To Death
Pokedex entries, particularly those in the first few generations, are often nightmare fuel that makes the player wonder why in the world someone would want to be a Pokemon trainer in the first place. One such entry comes from Gold & Silver, which states that a lick from Haunter will cause a person to shake uncontrollably until they die, which is a morbid feature on a Pokemon known for licking. This entry carries over into future generations, though normally without the mention of death by Haunter.
4 It's Said To Be From Another Dimension
Being the only Ghost-type Pokemon found in Kanto, it's no surprise that the Gastly line is looked at through a mystical lens with professors all around the region trying to make sense of it. One Pokedex entry from Red & Blue speculates that, due to Haunter's ability to float through physical objects, it comes from a different dimension.
While it's definitely not an Ultra Beast, this doesn't mean that the Gastly line isn't from a different realm to the Pokemon world. A common theory is that Gengar is the ghost of a dead Clefable, though the reality is that it could be an alternate reality version of the Fairy-type Pokemon, which may explain why it can learn Fairy-type moves.
3 It Has Appeared In Nearly Every Regional Dex
Before the international gaming crisis that was Dexit, the majority of Pokemon appeared in either the regional or national dex in the first seven generations. This did change in Black & White, but it wasn't nearly as exclusive as the Galar dex was for Sword & Shield. While the Gastly line has appeared in every regional dex in the series so far, it wasn't a part of Unova's regional dex until Black 2 & White 2, where it could be found in White Forest in the post-game.
2 The Diamond & Pearl In-Game Trade
In-game trades in Pokemon aren't always the best use of caught Pokemon, but there are some hidden gems that players should take advantage of more often than not, such as the Hawlucha trade in Ultra Sun & Ultra Moon and the Machop trade in Gold & Silver. One trade that is definitely not worth the hassle is the Haunter trade in Diamond & Pearl, where players can exchange a Medicham for a Haunter. While this seems like a sure-fire way to get a Gengar without an additional console, the trainer in question seems adamant in ruining the player's day as the Haunter received is holding an Everstone, preventing it from becoming an all-powerful Gengar.
1 It's Used Competitively
Gengar has been a popular competitive choice since its debut, with its high Speed and Special attack making it a decent glass cannon sweeper that was made even better in generation three when it received the Levitate ability. However, in generation seven, Gengar took a massive hit by losing this ability and having it replaced with the inferior Shadow Tag instead. Since Gastly and Haunter retain the Levitate ability, Haunter has been seen some competitive holding Eviolite to improve its middling defenses alongside support moves like Will-o-Wisp and Icy Wind.