Pokemon Stadium - Gym Leader Castle Round 1 - Transfers ONLY from new game (Red) FAQ:

Q: What is this run?
A: Basically, only use transfers to beat Round 1 of the Gym Leader Castle in Stadium 1, while starting from a new file of Red. So you have to play through the game and build a team to the point you then beat the Gym Leader Castle.

The reason it is transfers only, is because otherwise the fastest method would be to to just use Rentals to avoid the team building altogether.

It is also glitchless, as it would otherwise be a joke, given the glitches that are possible you can completely destroy the point of the category, or make a perfect team in minutes

Q: Why are you using Red as the game to get transfer from?
A: Red over Blue because I'm using Nidoking, and Nidoran Male is more common in Red.
Red over Yellow is basically the same, Red is just a bit faster in game. The main difference is actually in the Stadium part - the final Rival fight in GLC changes his team based on the team he has in game if you use a transfer pak. So he'll have a Venusaur main team playing from Red as I pick Squirtle, but in Yellow he'd have Flareon or Vaporeon, which are more annoying to kill.

Q: How are you going so fast in Red??
A: That's the Dodrio Tower, a mode in Stadium 1/2 that lets you play RBY at 4x speed, as long as it's connected with a transfer pak.

Q: Is Pokemon Stadium 1 from a new save file as well?
A: No, otherwise you couldn't use Dodrio Tower.

Q: Will you do a run of Complete Game with transfers from new game like this?
A: No, because grinding to L100 from Prime Cup would be insanely boring and not fun.

Q: Will you do other cups/parts of the game like this?
A: Yes, I plan on doing Petit Cups too, as well as Little Cups in Stadium 2. Might also do other GLC and Poke Cup stuff, we'll see.

Q: What is the route for the team you want to make?
A: For Gym Leader Castle, the Pokemon you fight are at at least Level 50, and match your highest level. As such, I want to make a few Level 50 Pokemon.

I'm going to only get 3 of them, and hope they are enough

Nidoking (Used throughout the game, caught at Level 3/4) 
Zapdos (Caught at L50 in Power Plant)
Articuno (Caught at L50 in Seafoam Islands)

Q: Are there any other Pokemon you considered?
A: Yes, but your options are limited on what you can get to a high level reasonably quickly.

At L50, the only other Pokemon to consider are Starmie (Can be caught at L40 in Yellow), and Moltres (L50 catch but in Victory Road, which I don't get to)

Mewtwo would be amazing if caught at L50, but given it comes at L70, it would raise all opponents to L70. As such it would have no support and have to win basically by itself. It also doesn't Amnesia until L81, which would let it wi a lot of the fights by itself, but is a serious time sink at that point.

Q: Do you know if this will work?
A: Nope, just mapped out a general idea purely based on theory, I've done no testing at all. Given the nature of this run using multiple games and a transfer pak, the way to test this is with a run