Pokémon Red and Blue: Cerulean City Gym

The gym is laid out as a pool with a walkway for you to get across. The first gym trainer approaches you from the water. He is a Swimmer who uses a Horsea and a Shellder, at level 16. Shellder is very defensive and knows Withdraw, which can make it more so.

After defeating him, head north, toward the gym leader, you will be approached by another trainer. She is a Jr. Trainer♀, who uses a single Goldeen at level 19. It knows the Flying-type move Peck, along with Tail Whip and Supersonic.

After defeating her, talk to Misty.

Leader Misty		Cerulean City Gym		2 Pokémon		P2079
		Staryu		Water		L18
Tackle	Normal	Water Gun	Water
		Starmie		Water/Psychic		L21
Tackle	Normal	Water Gun	Water	Harden	Normal	BubbleBeam	Water

Staryu is an easy defeat at the hands of Bulbasaur, Pikachu or Rattata. Misty's strategy is to use an X Defend to boost Starmie's Defense, while it destroys you with BubbleBeam, which has a chance to confuse even if it doesn't knock out your Pokémon. Hit it with a Leer to cancel this out, then destroy it with Vine Whip, ThunderShock, Hyper Fang or Mega Punch.

Upon defeat, Misty will award you with the CascadeBadge. She will also give you TM11 which contains BubbleBeam. There is only one in the game, so use it only on your very best Water-type.

When you're done, exit the gym and head north onto Route 24. If you already traversed the northern routes, then go through the house in the northeast part of town toward Route 5.

Advance to Route 24

Advance to Route 5