First off this isn't my idea so I won't take credit, I saw it on cheezeburger but can't remember the original poster.
Now if like me you've finished this game several times and want to try something different but are sick of the same old nuzlocke ending with whitney try this Avatar; legend of aang/korra meets pokemon hybrid.
The rules are simple
Rule 1 - choose your nation. The nation you choose at the start will dictate which pokemon can and can't be.
Fire nation can use fire, electric, dragon and dark types Water nation can use water, grass, ice and poison types Earth nation can use rock, ground, steel and fighting Air nation can use Flying, bug, psychic and ghost
Rule 2 - you can only use pokemon from your nation. A pokemon with a different type may be used as long as it gains an appropriate secondary typing on evolution. For example a snover can be used by air nation if it evolves into frosslass as soon as it can.
Rule 3 - normal pokemon can be used by anyone unless they have a secondary typing in which case that typing will correspond with each nation.
Rule 4 - you are not the avatar
I think that covers it. I highly recommend trying this as it is a lot of fun.