Nuzlocke Challenge 1.) Can only catch the first Pokemon in each area and nothing else. 2.) If a Pokemon faints it is considered dead and must be released. 3.) Nickname all your Pokemon to grow closer bonds with them.
A couple other rules you can add to further vamp up the challenge. 1.) No catching duplicate Pokemon, thus ruining most routes if it is something you already have. 2.) No buying any items. 3.) Battle style is on Set. 4.) No Pokemons level can be higher than the next gym leaders highest level Pokemon. 5.) If you white out it is a game over.
I played through a Nuzlocke with that ruleset and it gave me DS snapping frustration with certain fights.