Psychic, and if you're talking about the gym leader from Hearthome City that uses Ghost Pokemon, then no.
Water type are good against fire and ground and rock type . Ice are good against grass and water and phychic. Hope this helps! :)
Ghost-type Pokemon are strong against Psychic-types. This is because Ghost-type moves are super effective against Psychic types, giving them an advantage in battles. Additionally, Dark-type Pokemon are also strong against Psychic-types.
After you get the HM and earn the Fantina in the Hearthome City Gym
Ok, Now Fantina is a user of Ghost types, I suggest catch a shinx and train and evolve it in to a luxio and make it learn bite, just try and use dark types against her -good luck-spyro king-
Psycic type is good against Dark type, if you are playing Pokemon platinum then you can get a Ralts outside Hearthome all you need to do is train it up to lvl 26ish and it will help lotz with Fantina This will have the opposite effect. Psychic is weak against Dark, and even so, the Gym is GHOST. In addition to this, Psychic is also weak against ghost, so use a good fighting or bug type. Machamp or Scizor are good choices.
exeggutor is good have it know two phychic and two grass moves
Good against steel Pokemon are fire and water Pokemon.
fighting is good against normal Pokemon
Flying type Pokemon are good against normal Pokemon.
The elite fours Pokemon are all lvl 50ish so have a good team at about lvl55+ and you should be okay I recommend taking a dark Pokemon because it will be super effective against two of them the elite four are types are, ghost phychic dark and fighting you can fight them in any order you want
Ghost pokemon are good against psychc and ghost.
you have to go to celestic town and see the elder and the ruins and then she will give you the HM surf so teach it to your Pokemon (you don't have to but it works good on fantina's Pokemon) and when you et back the platform will be down. the doors you go in are right, middle, left, right and you are at fantina hope i helped ;p angelbaby17