Original Gold Whitney - That Miltank came out of nowhere and hit my party like a ton of bricks.....constantly....almost made me throw my cartridge around .

Blue/Red Koga - Use Toxic one more time, I dare you, I double dare you M*********!!!.

Pokemon Stadium 2 (Gym Leader Castle) Lance - While not particularly hard per se, the fact that you had to go through 4/5 very difficult battles before fighting him without having the chance to earn any continue would force you to be almost perfect.

I must be one of the few people that actually enjoyed Morty. Yes his Gengar was OP, yes Shadow Ball was overkill, but a Rattata could steamroll him. Once it's Hypnosis PP was depleted, it was game over.

I never played any of the 2nd gen games before Soulsilver came out. Anyhow, I didn't find Koga in blue to be as hard as others say. If I remember correctly, I had an Nidoking.

I never head an issue with Morty. Whitney and Elisa, very much yes.

I think i also had trouble with either the Steel or Ground guy in White.

There you go . If you had a Poison type on your team, you'd be set. If you didn't, then Koga would proceed to Toxic-rape your team with his lvl 43 weezing, laughing through your switches as he proceeded to Smog your incoming poke.

Once he handed my own ass to me for the bajillion time, I decided to get myself a Rhyhorn from Safari zone, grinded like a madman till it evolved to Rhydon and then used Dig like there was no tomorrow. Granted, I could have done that from the get go, but those were my noobish days with Pokemon games XD.

I agree on Whitney. Rollout makes me want to put my head through a wall.

Volkner (Gen4) has been the only gym leader i've had to fight more than 3 times, but it was awesome, i love to fight leaders and besides him no one has ever been particularly annoying, i love them all!!! :D - no least favorite.

I always had huge problems with Koga, but I don't think I was aware as a child that poison was invulnerable to the poison condition xD

Saw the thread title and knew it would be you Radish :P

I agree with a lot of what you have on here but then I gave you suggestions and influenced you (he didn't even remember who Candice or Fantina were before I told him :P )

Sabrina in RBY. No way to exploit her weakness, and it's not like you can have a pokemon resistant to Psychic with a decent move their pokemons don't resist.

I didn't have problems with Whitney because I had a Fearow with STAB Return already :P

Although she was much harder on Yellow (her level 50 Alakazam is way too OP), she wasn't that hard if you had a faster, more physical oriented pokemon like Arcanine and Persian (Persian especially, since the critical glitch would cause almost all attacks from it to be a Critical). 

Fearow with STAB Return on Whitney? That's massive grinding XD.