Take a Gastly as a main mon, his name will be EvilEyes. EvilEyes, in opposition of it's name, and what you should believe when hearing it, is a coward. He/She always runs when encounter a pokémon with intimidate, pressure, dark types or another ghost types(it's too scaring) and can't learn Mean Look.
But you're a good trainer, and as a good trainer, you must show your pokémon his/her place as a ghost pokémon. So, he/she must solo Fantina's Gengar(this is when the ghost exception finishes). After it, he evolves into a Bad Haunter. This guy is sooooo bad. He must learn Mean Look(or remember it in Pastoria) and must use it at the start of every battle. Intimidate and Pressure are for the weak, so, he must solo every pokémon with this abilities now, and the ghost types too, because he/she is THE ghost type. But he still have a problem, he hates the possibility to face a Dark Type pokémon, because they can kill him. So EvilEyes, when a Haunter, will never face a Dark Type...
...Until Candice's Sneasel. You decided that it's time for your pokémon to KNOW he is a Ghost, and as a Ghost, HE CAN HAVE NO FEAR. So, he must face the most difficult dark type pokémon before the Pokémon League. Candice's Sneasel is the best choice!!!
After it, EvilEyes evolve into a BIG AND BAD GUY, he/she is cruel. He is so cruel, that he decides to forgot Mean Look, he/she already have a Mean Look...it's so freckly natural!!!!! He/she decides to go deeper. It's time to think in the after death! He/She decided to learn Destiny Bond, because, IF he/she dies(correct me if I'm wrong, when your pokémons die in your scramble, it's really dead, right?), he/she must know the killer will go whit it for it to revenge kill him/herself in the hell. The intimidate/pressure pokémons and ghost types obligations ended when he/she evolves. This is past, he showed to everybody he/she is the best ghost and no one scares it anymore. He/she wants just one more quest: KILL THAT LUCIAN'S MOTHERF****G ALAKASAM. It's a crap, and stinks. He/she must solo it.
After it, it has no more obligations. The world belongs to him!
In BPR, the Haunter's obligation to fight Ghosts and Intimidate/Pressure mons continues.
Hope you liked it, and have fun!!!!