Main rule change
As opposed to the rules for traditional nuzlockes this one revolves around the typing of the last Pokémon you received (only for the starter) or caught within five tries of a route. The Pokémon you can catch needs to be within the first 5 encounters of the route and weak to the last Pokémon you catch or your starter at the very beginning. If you find one of the types you can catch on the first try but can't catch it your 5 encounters are gone for that route. The rules for fainted Pokémon still applies as normal so if it faints it's "dead".
Typing issues
Because normal has no super effective typing its a wild card for any type except Rock, steel, and Ghost type Pokémon. However if a normal type has another type like flying you won't get this bonus as it will act as a pure flying type or it's other type. It's only a wildcard as a pure normal.
Dragon can only allow you to catch Dragon types so pure dragons will most likely cause a game over if you're not careful enough.
Adding types through soak, Trick or Treat, and other methods do not make a Pokémon catchable despite them potentially being weak to the type you can catch.
Mega Pokémon are not counted so charizard will only act as a fire Flying type despite being dragon in Its X mega form.
Example
Let's say you start off with Torchic in RSE the types you are only able to catch are bug, steel, ice, or grass. On the first route you go to after being able to catch Pokémon you find a wurmple (a bug type) and you managed to catch it within 5 encounters in that route. the new type you need to catch needs to have a type that is weak to bug (aka grass, psychic, or dark) the next route you don't find any of these Pokémon within your five encounters but find a seedot on the next route and catch it. The type is now grass that the next Pokémon needs to be weak against but you find a nincada instead which is 1x to grass. But it's also ground and grass beats ground type Pokémon so it can be caught despite being part bug and 1x to grass. The multi typed Pokémon just need to have one of their types to be weak towards it. doesn't matter if the primary /secondary type resists it. Continuing on your nincada happens to evolve into Ninjask (and Shedinja) and you haven't caught another Pokémon yet. The new types you can now catch must be either weak to Flying and bug, or Bug and ghost. If you choose Ninjask's typing of flying you can't catch a Pokémon weak to ghost and vice versa. Ground gets discarded as neither Ninjask or Shedinja have that as their typing despite you having caught them as nincada. Evolving your last Pokémon can cause the typings to be replaced, removed, or added to the typings of what you can catch.
Mis
Every other rules for nuzlockes can apply including the optional ones.