His gym will be a old abandoned theatre. Lots of dark wooden floors and (ripped) purple wallpapers. The path leading to him will be a maze in between the audience chairs. Just like that feeling you have when you try to get to your seat in a full cinema...
Anyway, there will be 5 trainers in the Gym, and they will use 1 to 2 pokémon each. Varied from: Shuppet, Drifloon, Litwick, Phantump and Honedge. They will sometimes block a path so you have to take an entirely new path. At last! You will get on stage, and there he will be waiting. "To win, or not to win? Lets find out!" And the Battle starts.
His second pokémon will be Gourgeist with Trick or Treat, Shadowball, leech seed and bullet seed.
The first of four Pokémon will be Banette! Banette will know moves like Shadowball, Phantom Force, Grudge and Feint Attack.
Third is Chandelure with Shadowball, Flamethrower, hex and Will-o-wisp.
And last, the pokémon that makes the gym complete: Rotom! But, every time you battle him, rotom will acquire a random form! You can't really prepare for that, so you will have to Improvise!
His moves will be Shadowball, shockwave, uproar and the move he gets with each form.
When you defeat Yorick you get the Jest Badge, shaped like a skull wearing a jester hat. Also you will get Shadowball as a TM.
Yorick has of course more "Acting" pokemon, but he won't use them in Battle. They work alongside him in the theatre.
He has two Frillish, nicknamed Romeo and Juliet
Doublade and Honedge
a Yamask and Cofagrigus
Multiple Gastly, 2 Haunter and a Gengar
A Duskull and Dusknoir
And also a Ditto,
Noctowl (Who helped him catch his first Ghosts)
and Mr. Mime
Pokemon is owned by Gamefreak/Nintendo
Yorick is my own