Gym Leader. Definitely. Now, I know this will be a long post. I'll state that now. My gym will be heavily involved in the storyline of the game. Unlike some that you need to beat just because that's how it works. My gym is actually attacked by the "team" of the game. I'm the 6th gym, and my gym is where the storyline starts cracking down to focus on the "team" of the game. IRL, I'm heavily influenced by storyline so I chose the gym to be heavily influenced by it as well.
Type: Steel
Pokemon:
Steelix lvl 43
Aggron lvl 49 ;306;
Metagross lvl 47
Steelix lvl 44
Excadrill lvl 46
My gym is in a lighthouse, like the Olivine city lighthouse. It consists of you going up through the floors after waking my team that blocks the staircases. Or the elevator... In case of Aggron. The story just made the gym fall asleep in an attack by the "team" of the game. Whether it was Team Rocket or Team Galactic or whatever. They attacked the gym with large amounts of sleeping powder to steal my pokemon, but they'd need my pokeballs that are on my person for that. Outside, your rival hands you a gas-mask to deal with the gas and traverse the gym.
First, you'd have to wake up my Metagross that is blocking your path to the stairs heading upwards, waking him up by ringing a large bell above the middle of the room. Metagross is a heavy sleeper and you'll need to ring it 3 times, each time waking up one of the "team" members (caught in the sleeping powder blast) that battle you immediately for waking them up. They disappear after you beat them. No special Challenge or puzzle, simply beat 3 trainers.
The next floor is pitch black and you would have to reconnect 2 energy sources to the light switches to turn them on and wake up my two steelix's. The lights startle the first one into shaking its head when it wakes up, smacking my single trainer on the head and waking him up, instead of battling you, he asks if you're alright after the attack on the gym. Your rival puts a gas mask on him so he stays awake and then heads downstairs to "protect" the Metagross from floor one. The second steelix bangs his head into the wall on waking up (by accident) and lets enough light in to wake up the second trainer on the floor. This one is from the "team" and the other trainer you woke up takes to fighting him. Little bit of a puzzle, no trainers you have to battle.
The floor above was fitted for my Excadrill, it's got a thin floor like the ice of the Sootopolis gym in Emerald, but only in some patches. There is a giant boulder blocking your path with Excadrill sleeping next to it. You will need to start cracks on the floor around the boulder to make it fall through the floor and land almost perfectly so that you can walk on it to the floor upstairs. ALMOST. You can't walk on it just yet. You have to wander around the floor, careful not to step on the same place twice and fall down to the floor underneath in places, until you get to the other side of my excadrill and roll him over onto the boulder, then the boulder will flatten out. While Excadrill is still asleep, head over to the other side of him and push him back to where he was, as the side opposite of him has barely enough room for you to walk through. Now, you can calmly walk over the boulder to the floor above. Large puzzle, no trainers.
On the final floor, my Aggron is sleeping right in front of an... elevator?! That's right, I put an elevator in the gym on like the 4th floor to go to floor 7 so that you can face me directly after dealing with Aggron. And the "team" members are swarming the floor, they're mainly just pissed off because they can't get up the floor, since Aggron is in the way. After first heading up the stairs, 2 grunts battle you back-to-back. Then, you need to walk around a cluster of them using attacks on the Aggron in an attempt to make it move. (Talking to any will tell you that you probably shouldn't do that in an attempt to stay incognito.) After that, you head over to the rest of them and fight a good 3 or 4 more before fighting the leader of the attack. The storyline part in my gym finishes up when you beat the "team" leader/commander/whatever and then he rips off your gas mask. You pass out from the sleep powder spores left from the attack. A few minutes later, you wake up to the sound of Aggron and the rest of my team on a rampage against the invaders. Then I (the gym leader) walk over and help you up, handing you your pokemon and saying that I saw a grunt take them off of you. I thank you for everything you've done and say that the enemy is long gone now. My gym is a mess, though. I welcome a gym challenge and bring you downstairs to the outside of the gym, where your rival is standing there. I say that if you want to gym battle, I'll stand right outside of the gym, as a service to the people who helped save my gym. Your rival starts his battle with me while you go off and do... whatever you have to do. Just enter a building and then come back to us and I'll congratulate your rival on a good match but tell him to watch for my Aggron next time. He walks over to you and tells you to be careful against me, since he just lost. I heal my pokemon and await your match.
I'd probably talk half-asleep and be wearing loose-fitting and comfy clothes. I'd thank you for your help dealing with the grunts and say thank you to you and you rival for making sure my pokemon didn't get stolen. Afterwards, I'd hand you the *Crash* Badge and *TM__ (insert name of move here)* as the other gym leaders (aside from the almighty #8) walk over and ask if the three of us are alright. I'd yell at them for being late and etc. I'd be pretty pissed against the "team" and want revenge for my gym. The trainer on the second floor would constantly stand in front of my gym from then on, blocking the entrance until after the game was over. For an end-game second match against me, my gym would be back to normal... Sort of...
During the final battle against the "team's" leader I'd show up with the rest of the gym leaders and I'd be especially pissed off while the gym leaders ravage the "team" along with you. I'll be using my Aggron in the open-world matches, And if you pay attention, you can notice me using a Magneton as well. (for my end-game match I have a Magnezone.
END-GAME TEAM!
Magnezone lvl 76
Skarmory lvl 75
Aggron lvl 79 ;306;
Scizor lvl 74
Bisharp lvl 77
Lucario lvl 76
Just the match, well my single trainer would be on the bottom floor, blocking the path to a newly-put-in elevator leading straight to me. But, security tape is blocking the stairs up for the rest of the gym, so it's just the 2 of us, and the other trainer is pretty weak compared to me. You'd have to fight my single, faithful trainer before heading up to the top where I am standing there, ready for the match.