Kanto, 1st Gym (Rock) + (Grass = x4 on all the pokemon)
Kanto, 2nd Gym (Water) + (Resistence and x2 Damage)
Kanto, 3rd Gym (Electric) = (You can't hit for x2 but you can resist and status)
Kanto, 4th Gym (Grass) - (Unless your a higher lvl, you will always be outsped and status'd)
Kanto, 5th Gym (Psychic) - (Since you are Poison type aswell, Psychic can hit you for x2, you can't status it (besides from Leech Seed) because most of the Psychic's have Syncronise)
Kanto, 6th Gym (Poison) = (They can't Poison you, but you can't dish back. You can Stall with Status though)
Kanto, 7th Gym (Fire) - At this point in the game,there's no way Venusaur can be dishing out on this gym. Unless he is level'd enough to take a Fire Blast or you like to risk the miss, you will die in out hit
Kanto, 8th Gym (Ground) = Yup, even with the Type advantage, this won't be easy. Ground hit's you for neutral and 2 of the Pokemon in this gym take Neutral from Grass and Cannot be Poisoned (Nidoking and Nidoqueen)
Elite Four, 1st (Ice) = (Even though they have the type advantage, 3/5 of her team is Water and you can strike back)
Elite Four, 2nd (Fighting) + In his team, you either resist his STAB's or hit Super Effeccctively.
Elite Fout 3rd (Ghost / Poison) - Every one of her Pokemon are Faster and can Status you back, in addition, she has a Golbat which resists every move you have, bar Strength.
Elite Four 4th (Dragon / Flying) - If I recall correctly, every Pokemon, bar Gyarados, has a SE move against you. You could try a Growth Set Up on Gyarados, but after that you won't get far.
Champion (Diverse) - Pidgeot beats you, Alakazam Beats you, You beat Rhydon, Eggexutor Beats you, Gyarados is equal, and Charizard (obviously) beats you. Unless you have a Rock / Electric Partner, this is Checkmate (Those types hits 1/2 of his team for SE)