how to beat morty

You need to have a Pokemon that is level 80 or higher and use a Pokemon that knows eruption or explosion.

you could have a dragonair and teach it Draco Meteor
that will kill almost anyone

get a high level ratticate with bite since ghost dont affect ratticate and dark is super effective its a good move

I beat the whole gym using a Kangaskan with a decent level and the ability scrappy. i needed some help at the end, though.i <3 quilava~

You should use a typlosion.

If you are talking about the first time (non rebattle) you only need a few Pokemon lv. 30 or so growlithe works well because of bite but you can get a fire stone at the pokeathalon dome. If you have anyone normal teach it different moves and shadow ball dosent work

Needed:
Heartgold or soulsilver version
A normal type Pokemon with tail whip and all other pokemons
How:
First defeat the gastly and haunters and if morty sends out gengar switch to your chosen normal type Pokemon and use tail whip. In HGSS he will use sucker punch but it will fail because tail whip is not an attack move. I had an Eevee Level 5 with tail whip here. And when he's out of usable moves, switch to your powerful Pokemon coz he will use struggle fainting your pokemon. Finish the rest off with the powerful pokemons.

A good strategy in heartgold and soulsilver is to use the Togepi, hopefully a Togetic by then, and use sweetkiss and yawn on his Gengar. After that, keep using extrasensory on it. Alternatively, using a Stantler, which I believe can be caught nearby if I remember correctly, will provide stab psychic moves and immunity to ghost type attacks that can be thrown at it. Other possible strategies include having an Umbreon with bite, Croconaw with bite, Drowzy, Kadabra/Alakazam, Gyarados, or even perhapse a scyther with persuit from the bug catching contest.