Fifth Gym Help

I'd sa train the Pokemon you have now it was a tough challenge for me but I did it just barely I had Empoleon as my starter who did you pick

Now I have some mayby you kan use this move,s:
Crunch
Bite
Punishment
Mayby you use some ghost type attack,s

First ask your friends if they have dark Pokemon and then trade wth wi fi if not catch some or lvl up you're own

Ghost and Dark Pokemon are handy for this battle. I would highly reccomend something like Drapion, Stunky/ Skuntank, Haunter, or Murkrow/ Honchkrow, but other ghost and dark Pokemon work well, too.

Drapion should know Crunch.
Stunky/ Skuntank should know Night Slash.
Haunter should know Shadow Ball.
Murkrow/ Honchkrow should know Faint Attack/ Night Slash/ Dark Pulse.

Any other ghost or dark Pokemon that knows a ghost or dark move also works fine.

Besides the Pokemon, the levels are pretty vital. As you've mentioned, you have a wicked low team. As long as your Pokemon are arount level 40, or at least the one(s) you'll be using for this battle, you should do fine. If your Pokemon are below level 30, you might have some trouble with this battle. Obviously, a good answer is to level up your pokemon. You can battle the trainers in this gym, for example, for awesome practice against Fantina. You also might get a couple levels on your pokemon.

Try trading or catching a gastly or haunter. (there is a rumor that you can catch a gengar in the old cheatue in eterna forest) (the room with the red eyes (man that creeps me out)) or try teaching a Pokemon a dark or ghost type move that might help and raise your pokemon more

I advise getting a Pokemon that knows a move you can use agaisnt her (drifloon) can be caught outisde the valley windworks building on thursday nights. Or murkrow which can be caught at that old chateau.

Anything that has bite would be perfect Bite is a very good dark move and you can't go wrong.