Nuzlocke

Basic rules
You can only catch the first encounter per route.
All Pokemon who faint are to be considered dead and released or boxed.
All caught Pokemon must be nicknamed to form stronger bonds

Optional rules
Dupe clause: if any first encounter is either an already caught Pokemon, or evolves into a Pokemon you have already owned, you may continue searching until finding a new encounter
Shiny clause: any shiny Pokemon encountered is available for capture
Static/event Pokemon: no Pokemon given freely should be used in runs. Pokemon obtained in trade and static (mostly legendary) Pokemon are banned from runs, on the grounds of op

Alternative, personally unused rules
White out clause: any time the trainer whites out/blacks out should be considered a failed run, and restarted