Pokemon Stadium counts, right? Because that Lass in Pika or Petit Cup with the god damned ToxicWrap Tentacruel... dear lord. Dig Arcanine was a troll, too.
Yeah, there were quite a lot of Wrap-based teams you had to fight in the original Pokemon Stadium. Probably the most annoying thing about them was simply how long it took. In the Gameboy games it took a few seconds to get through a Wrap cycle since the animation was very short and you could keep mashing A. In Pokemon Stadium they went on forever.
That Lass also had a Gyrados. Tentacruel and Gyarados had really high Special Attacks in these games, so Surf, etc. would hit really hard.
I'd say the battle right afterward was even harder. In particular the Dragonair with Thunderwave, Wrap and Dragon Rage. Basically the only things that can beat Dragonair is something that has more than 40 HP and a higher Speed stat, and considering the restricted pool of Pokemon you get to choose from... And even when you fulfill those requirements, you still often can't OHKO it, even with an Ice Beam. I suppose the best thing to do would be to fish one of those L.15 Dragonair from the Safari Zone in Pokemon Yellow and train it to L.20 to beat it (and the rest of the tournament for that matter) lol.
For RBY, the only gym that ever really gave me any trouble was Brock, and that's because I usually started with Charmander - if I started with either of the other 2, he was easy as well. Saying that, once I figured out you could catch and train a nidoran male to 14 (I think?) and get double kick, Brock became a pushover as well.
I never found Brock too hard in Red. Even with Charmander. Onix's Special is so low that you can power through it with Ember, and if you manage to burn it, then it basically KO's itself once it uses Bind. Not to mention you can weaken it with Growl, Tail Whip/Leer, Sand Attack, String Shot from your teammates. Even if you got a Weedle, you can Poison Sting a few times to get it poisoned, then you just have to stall it out (which is easy since when it uses Bide it sits there for 2-3 turns doing nothing and Bind doesn't do much damage).
Pokemon Yellow is much, much more difficult. There's no Weedle available in the wild, and the only special move you're likely to have at that point is Thundershock, which Geodude and Onix are immune to. So the best thing to do is use Tail Whip/Leer 6 times, then wear it down with Tackle, Gust, Peck, Scratch and Quick Attack from your team (you get L.9 Pidgeotto in Viridian Forest, but even those struggle a lot against Geodude and Onix). However, there are Mankey that learn Low Kick at L.9, Nidoran that learn Double Kick at L.12, and you can evolve Caterpie to Butterfree where it learns Confusion at L.10. However, all three of those examples require over-training. Generally my team would be in the L.6-L.8 range when fighting Brock.