* Bring Ghost-type Pokémon. Ghost-type Pokémon are ineffective against other Ghost-type Pokémon, so it's helpful to bring some Ghost-type Pokémon with you. Good options include Haunter, Gengar, and Misdreavus.
* Use strong attacks. Ghost-type Pokémon are weak against Dark and Ghost-type attacks, so it's important to use these attacks whenever possible.
* Be careful of status effects. Morty's Pokémon can use a variety of status effects, such as Will-O-Wisp and Curse. Be sure to heal your Pokémon if they become afflicted with a status effect.
* Don't forget to use items. Items can be a big help in battle, so don't be afraid to use them. Potions, Super Potions, and Full Heals can help keep your Pokémon healthy, and X Attack and X Defense can boost your Pokémon's stats.
If you follow these tips, you should be able to beat the Ghost-type Gym Leader and earn the Ghost Badge!