I just can't get into Nuzlocke challenges. Too many rules.
I think the three main rules are like,
Have to nickname your pokemon so you feel attached to them (for the extra emotional blow if they die)
Can only catch one pokemon per route, if you flee, kill it or it flees you cant catch anything else in that route and move on
Your pokemon die, you can't use it.
Some people do add other little rules, I know someone who doesn't heal with potions in gym fights, or for instance for me, to avoid catching the same pokemon in another route; if I have already caught it i can flee (not kill, I stick to that rule) and walk around for another kind of pokemon. One even decides to release his pokemon when dead, but I just put them in PC boxes since my games are the physcial versions and rather keep them after finishing a game.
I get it does sometimes feel a bit much, and cause we're used to just playing normally, we forget to keep an eye on matches, for example, if you odnt take into consideration that the enemy pokemon just used too much leer that could instantly kill your pokemon if they decide to attack.
I'm personally okay with the rules, but I get wayyy too attached to my Pokémon to do Nuzlockes. I attempted one, cried when a Pokémon fainted and gave up.
Definitely the main point of the game, to feel more attached to something that could not end well.
I just lost a good pokemon in my Pokemon X nuzlocke to which I decided to make a POkemon Y nuzlocke instead XD I'll get back to X at some point. XD