What type of Pokemon can beat ghost type Pokemon?

Answer 1

Offensively, Dark and Ghost type attacks are super-effective against Ghost-type Pokemon while normal and fighting deal them no damage. Bug and Poison type attacks deal halved damage to Ghost-type Pokemon.

Defensively, Dark and Steel Pokemon take halved damage, from Ghost-type attacks. Normal Pokemon take no damage from Ghost-type attacks, and lastly ghost and psychic Pokemon take double damage from Ghost-type attacks.

Some Ghost Pokemon with notable Dual-Typing:

Gastly, Haunter, and Gengar: All Three are Psychic-Poison type with Levitate as an ability. They gain an immunity to ground type attacks and gain a Psychic weakness. This trio spawned rumors that Ghost-type Pokemon were weak to Psychic-type attacks, which is untrue.

Sableye, Spiritomb: These two are Ghost-Dark which means they don't take double damage from any attack unless a move like Foresight is used to negate one of it's defenses.

Shedinja: This pokemon has only 1 HP and has a Bug-Ghost typing. It also has the ability Wonder Guard which makes it so that if an attack is not super-effective against Shedinja, it doesn't hurt it. Weather effects (hail, sandstorm) and entrance effects (stealth rock) still injure it, which causes instant death to Shedinja. A Fire, Ghost, Dark, Rock, or flying type attack will kill Shedinja.

Rotom: Ghost-Electric/ Grass/ Ice/ Water/ Fire/ Flying and has the Levitate ability. Rotom's type corresponds to what form he's in (if he resembles a fridge, he's in his Ghost-Ice form, for example) so act accordingly. Ghost and Dark type moves will always hit for double damage, but his other weaknesses and resistances are subject to change.