The Nuzlocke Challenge is where you play through a Pokemon game, any of them. But there are some special rules. First of all, you may only catch the first Pokemon you see in each area. No more, no less. In game npc trades are allowed. If you kill the first Pokemon you see in an area, tough luck. The second rule is that any fainted Pokemon is considered DEAD. It must be released or never used again. Sometimes people put in their own extra rules, that range from hard (no items) to insane (no Pokemon centers). Usually, people use ones like no legendarys. Most people let shinies say "screw these rules". It may sound challenging but Nuzlocke Challenge is very fun. Feel free to post any experiences with the challenge, or some rules for inspiration to fellow Nuzlockers. I do highly suggest you try it though. Even if it is only once.