Ok I came up with an idea for a dark gym (I don't know of it was already thought up before, please tell if it has been), what if (as crazy as this could sound), the city (or part of it) is the gym!?
Now you all are probably wondering why the whole/part of the city would work? Well what if in daytime/noon the cover it with a dome to stimulate night (of course at night they wouldn't need the dome). The only lights available would be (sans the building lights, which everyone except the gym leader and his/her trainers woukd be inside) the street lights.
Under those lights, you will fight a trainer with special rules. For example one battle could be like horde battles, but much more difficult, for example you can only knock out one at a time (so no eq or rock slide). There can also be specific pokemon in your party that you can only use (say for example your 3rd or 6th pokemon i your party) or a certain time limit, you can't use items (held or not), or your opponent can take and use your items (Mega stones count but they cannot use them if they don't have the pokemon for it, also items of any kind are returned to you), or can double the money you earn/lose and last but not least inflict a random status ailment on one or all of your pokemon.
So yeah they can do 1-3 of these things that I mentioned. Now you guys are wondering 4 things; "How do I start this event?" "How do I exit?" "What happens when I lose?" "How do I find the gym leader?"
I will answer those questions around 1 as I have to get back to work for now. See you guys in a few hours. --- Persona!!!
Wow no one post on here? Anyway first off is how to activate the challenge, you just go to the old gym and talk to the gym leader (the person for the gym is the new 8th gym leader having recently recieved the position), he/she will activate the dome and tell all citizens to go inside (I know it sounds illogical to tell people to go inside their homes, but its pokemon what do you expect?).
How to exit is simple go inside a building, but however you will have to restart the challenge again, that means you'd have to battle the trainers again.
What happens to you if you lose is something like a pre warm-up for the E4. If you lose your pokemon get revived by the trainer who beat you, however the rules will change an their team might change as well, now this is where the earn/lose double money. If you win once you get double the amount of money, but if you lose once you earn the same amount and lose the normal amount. Lose twice and you pay them double and you get paid less half of the normal amount if you win (that would be the limit, also I know I left out the part where the money rule is an automatic rule).
How to find the gym leader in the maze is somewhat simple and random every time (he/she will be in one place and will not move) The trainers you beat will give you a hint but some of the 13 trainers will lie to you, tell you the truth or will just guess. There will be subtle hints as to who's lying or telling the truth.