Pokemon Fire Red & Leaf Green - Second Gym Leader Battle [4K 60FPS] 

Gym Leader Misty
Staryu Lv. 18
Starmie Lv. 21
Wow! Her Pokémon are far higher than the ones you have been battling much earlier. Even if you're at a good level, you still may get your ass kicked by Misty. Starmie is a very fast Pokémon and may go before yours if your Pokémon have crap speed. Both of her Pokémon know Swift, which will never miss under any condition. Also, both of her Pokémon know Water Pulse, which is a powerful move easily capable of confusing you. Highly annoying.
Misty has several Super Potions backed up in her pocket, and when her Pokémon are in the red zone, she will nearly fully heal them. If you want to avoid dragging out the battle, use an attack to get them in the low yellow, then follow up with a powerful attack to finish them off. Starmie can kill quite quickly, so do this tactic on him.
Once you win, you will receive the Cascadebadge and TM 03-Water Pulse. You can also use Cut outside of battle. We don't even HAVE that attack yet!