Catching 3TrainerPoke - Page 1
I found an alternate method of getting 3TrainerPoke with the Steal Trainer's Pokemon code. (010156D0 on Yellow version)
Don't know if anyone knows about this yet, it wasn't in the GlitchDex…
All you need to do is make sure you have it's PokeDex entry so it won't turn into a Rhydon. This can probably be done almost anywhere, but I can't test that now.
There are a number of ways of getting some glitches - for example, you can gameshark MissingNo., but we don't mention the multitude of ways you can gameshark it on its page. If it can be gotten without 'shark, we go with that method because it's more accessible.
The method outlined above can be used in R/B to get 'M, but there's really no need because you can just do the Old Man trick, for example.