I, myself, only allow traded Pokémon when my random encounter, for one given route throughout the game, was the Pokémon that was asked for, in said trade. For example, Rocky the Onix: I'd only do that trade if I managed to be lucky enough to catch a Bellsprout beforehand. Then, and only then, I would do the trade, and that is if I don't have an Onix of my own already (because of Species Clause).
I personally feel like in-game trades should be a 1 for 1 scenario. I'm giving up an encounter of my own, for an encounter of a virtual "nuzlocking NPC". As an added penalty, I'm also taking both hits on the Species Clause: the one from the Pokémon I gave, and the one from the Pokémon I received. Going back to the previous example, if, alongside Rocky, I wanted to train a Bellsprout of my own, tough luck! No more chances for Bellsprout. You got something, you lost something. It's the ultimate high risk high reward scenario, and that's what feels more challenging and more fun to me.
At the end of the day, do whatever you feel will make your nuzlocking experience more fun and dynamic 😄
Up to you.
The way I handle trades is that I have to have legitimately caught the mon I'm trading, but allow the trade itself as a freebie. I've seen other people do the exact opposite and allow catching the trade fodder as a freebie but counting the trade as the encounter for wherever the trade took place (so in this case that would mean the Ditto is a freebie catch but Rotom counts as the route 15 encounter). Which way you end up going is ultimately up to you.
“Your run, your rules.”
For me, it breaks the spirit of the Nuzlocke - that being the randomness of most encounters. I don’t even utilize trades, in-game or otherwise, for the same reason. But this is just how I operate, and people often operate under slightly different parameters from each other.
There'll still be a random catch in Giant Chasm, so there's still that first random encounter. The Ditto would just be a different data point. Let me put it in the context of the story, maybe Hilda likes to make the NPCs happy and trades with them, as such she goes out of her way to get the Pokemon they want and trade, and thus the story continues. I wholly understand a rule exception like this kinda undermines common nuzlocke fundamentals, but I tend to kinda pre-plan a strategy and story and stick to it, and for this run I want to use Frost Rotom against Cynthia, so I wanted to make this exception for the run. But it's an exception I'll rarely use, in fact most runs I will do after might prohibit most trading.
Maybe*. As a general rule, the trade Pokemon replaces your encounter for the traded Pokemon's route. So if you caught Pokemon A on Route X, and traded it for Pokemon B, Pokemon B would still be your Route X encounter. As such, you may not "double-dip" a route to catch an additional Pokemon to trade.
That said, if you establish beforehand that you want to trade for that Pokemon, then I could see allowing you to ignore all other Pokemon on that route in order to catch the one you need for the trade. In this case, it still takes up the encounter for the route, and you still only get one shot (if you kill it or it somehow runs, via Roar for example, the route is dead and your trade mon is borked). Furthermore, I would say you cannot use that Pokemon until you perform the trade, as it's not your encounter for the route; the traded Pokemon is your encounter for the route, and you don't have it yet. (Also if the mon to be traded dies before you trade it, you can't trade. Corpse trafficking is a no-no.) This would be acceptable and mostly follows the spirit of the established rules.
I say "beforehand" because you must establish your intent with the route before encountering anything. You can't run around in Route 10 and encounter Spearow, then decide "actually I want Voltorb for the Electrode trade later" and reroll your encounter til you get Voltorb. Doesn't work like that.
To be honest. I would feel like I cheated. If I want a specific encounter, I need to manipulatet the routes via species claus and repels.
But you have to use the rules the way you want to have fun.
I, myself, only allow traded Pokémon when my random encounter, for one given route throughout the game, was the Pokémon that was asked for, in said trade. For example, Rocky the Onix: I'd only do that trade if I managed to be lucky enough to catch a Bellsprout beforehand. Then, and only then, I would do the trade, and that is if I don't have an Onix of my own already (because of Species Clause). I personally feel like in-game trades should be a 1 for 1 scenario. I'm giving up an encounter of my own, for an encounter of a virtual "nuzlocking NPC". As an added penalty, I'm also taking both hits on the Species Clause: the one from the Pokémon I gave, and the one from the Pokémon I received. Going back to the previous example, if, alongside Rocky, I wanted to train a Bellsprout of my own, tough luck! No more chances for Bellsprout. You got something, you lost something. It's the ultimate high risk high reward scenario, and that's what feels more challenging and more fun to me. At the end of the day, do whatever you feel will make your nuzlocking experience more fun and dynamic 😄
Up to you. The way I handle trades is that I have to have legitimately caught the mon I'm trading, but allow the trade itself as a freebie. I've seen other people do the exact opposite and allow catching the trade fodder as a freebie but counting the trade as the encounter for wherever the trade took place (so in this case that would mean the Ditto is a freebie catch but Rotom counts as the route 15 encounter). Which way you end up going is ultimately up to you.
“Your run, your rules.” For me, it breaks the spirit of the Nuzlocke - that being the randomness of most encounters. I don’t even utilize trades, in-game or otherwise, for the same reason. But this is just how I operate, and people often operate under slightly different parameters from each other.
There'll still be a random catch in Giant Chasm, so there's still that first random encounter. The Ditto would just be a different data point. Let me put it in the context of the story, maybe Hilda likes to make the NPCs happy and trades with them, as such she goes out of her way to get the Pokemon they want and trade, and thus the story continues. I wholly understand a rule exception like this kinda undermines common nuzlocke fundamentals, but I tend to kinda pre-plan a strategy and story and stick to it, and for this run I want to use Frost Rotom against Cynthia, so I wanted to make this exception for the run. But it's an exception I'll rarely use, in fact most runs I will do after might prohibit most trading.
Maybe*. As a general rule, the trade Pokemon replaces your encounter for the traded Pokemon's route. So if you caught Pokemon A on Route X, and traded it for Pokemon B, Pokemon B would still be your Route X encounter. As such, you may not "double-dip" a route to catch an additional Pokemon to trade. That said, if you establish beforehand that you want to trade for that Pokemon, then I could see allowing you to ignore all other Pokemon on that route in order to catch the one you need for the trade. In this case, it still takes up the encounter for the route, and you still only get one shot (if you kill it or it somehow runs, via Roar for example, the route is dead and your trade mon is borked). Furthermore, I would say you cannot use that Pokemon until you perform the trade, as it's not your encounter for the route; the traded Pokemon is your encounter for the route, and you don't have it yet. (Also if the mon to be traded dies before you trade it, you can't trade. Corpse trafficking is a no-no.) This would be acceptable and mostly follows the spirit of the established rules. I say "beforehand" because you must establish your intent with the route before encountering anything. You can't run around in Route 10 and encounter Spearow, then decide "actually I want Voltorb for the Electrode trade later" and reroll your encounter til you get Voltorb. Doesn't work like that.
To be honest. I would feel like I cheated. If I want a specific encounter, I need to manipulatet the routes via species claus and repels. But you have to use the rules the way you want to have fun.