Being left by its original Trainer
With another Trainer
As revealed in A Chilling Curse!, Gengar was originally caught by a Trainer living in Vermilion City, three years before the events of Pokémon Journeys: The Series. However, as he started losing battles and failing to catch other Pokémon in Gengar's presence, the Trainer attributed his misfortunes to a curse caused by Gengar and decided to get rid of it. Before he abandoned it, he instructed Gengar to wait for him at the place that would later become the Cerise Laboratory.
As a wild Pokémon
Not knowing its Trainer had no intention of returning for it, Gengar obediently waited for its Trainer, even staying at the building as it was being converted into Professor Cerise's research center. It tried to scare the Professor off by haunting the building, but as he only found its actions amusing, it eventually gave up trying to frighten him.
Gengar debuted in Best Friend...Worst Nightmare!, where it resumed its mischievous activity by scaring Ren, making its presence known for Ash and Goh in the process. The latter tried to catch it, but Gengar simply deflected all of the Poké Balls he threw at it. It eventually fled when Chloe commanded Yamper to use Spark. It was later seen at the end of the episode, perched atop the Institute.
At the end of Raid Battle in The Ruins!, Gengar phased through the wall and watched Ash, Goh, and their Pokémon as they returned from Unova.
In A Chilling Curse!, Gengar once again began causing trouble at the Institute and subsequently hid in Ash's shadow. When Ash ran into Gengar's former Trainer, it overheard the latter bragging about how much he enjoyed being free from its curse. Angered by the revelation that its Trainer abandoned it, Gengar started attacking him. When the Trainer fled in fear, Gengar ran off as well. Team Rocket found Gengar and asked it to join them, but when it refused, they instead tried to capture it. Ash showed up, managed to free Gengar, and convinced it to fight Team Rocket alongside him. After Gengar defeated Team Rocket's two Dusclops, Ash collapsed from a fever he had unknowingly caught earlier. When Ash woke up at the laboratory, Gengar appeared and dropped a Poké Ball for him, indicating it wanted to join his team. Ash accepted the request and caught Gengar.
In Destination: Coronation!, Ash used Gengar in his battle against Visquez so he could increase his World Coronation Series ranking. Gengar substituted for Pikachu while going up against Visquez's Raichu, and it managed to defeat it with Psychic. Gengar then went up against Visquez's second Pokémon, Electrode, but was soon defeated, though not before dealing some damage on its opponent.
In A Festival Reunion!, Ash brought Gengar with him to Shalour City for a World Coronation Series Battle Festival Challenge. During Ash's match with Korrina, Gengar went up against her Mienshao and Lucario, getting defeated by the latter without managing to deal any damage on either.
In Sword and Shield: The Darkest Day!, Ash used Gengar to face a rampaging Gigantamax Coalossal alongside Leon's Dragapult. During the battle, Gengar saved the lives of a group of Workers who were nearby.
Personality and characteristics
Gengar was once loyal to its previous Trainer, obeying his instructions to remain at the future site of the Cerise Laboratory. Over time, however, Gengar became resentful of its old Trainer, even to the point of attacking him upon seeing him again and only calming down once he ran away. It grew bitter and developed a hostile nature against all humans, repeatedly attacking them with its powers. After it bonded with Ash and was caught, it became friendlier, though it still seems to have a mischievous streak, such as when it showed its concern for Ash by dumping a pile of apples on top of him, and when it scared Ren and Chloe in JN057 by phasing through a wall. Gengar dislikes being accused of something it didn't do, as seen in Panic in the Park!, when it appeared out of nowhere behind Ash and hit him with Shadow Ball after overhearing him accusing it of stealing Goh's Pokémon's food.
In battle, Gengar takes advantage of its Ghost-type abilities, allowing it to easily escape snares and confound opponents, as seen in Destination: Coronation!, where it was able to escape the tail hold of Visquez's Raichu simply by phasing through it. However, in the same episode, it was revealed to have trouble combating faster opponents such as her Electrode, and later Korrina's Mienshao and Lucario. Gengar also has the ability to become invisible and to disappear and reappear. Like all of its species, Gengar is also able to decrease the temperature of its surroundings, as seen in Best Friend...Worst Nightmare!; and hide in the shadows, as seen in A Chilling Curse!.
| Using Shadow Ball
| A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.