Easy, You Will Need A Surf Pokémon.
On The Deck , Use Surf And Swim around in the water whilst pressing " A " Soon It Will Say That You Will Have The missing Part.
P.S- If Youve Tried And its not there - Try The other pice of water.
You find her at the Cerulean Cape after you have defeated/caught Suicune from 4:00 PM to 5:59 PM.
You get it in the cave going to Cerulean City. You will have to fight a guy, and then he tells you he will share. However, you may only choose one.
You can find Mewtwo in the back of Cerulean Cave.
Cerulean cave
You can find ditto in cerulean cave.
You can get all the Pokemon in the cerulean cave where you find celebi below the cerulean cave.
On Cerulean Cape
cerulean city kanto.hope it helps!
In Cerulean City Gym.Superoo10
You have to look near all the floaties in the Cerulean gym and then once youfind it take it back to the power plant
Cerulean Cape after finding him on other routes.
It's hidden in the Cerulean Gym, in one of the inflatable life tubes.
In Violet City next to the PC in the Pokemon Center
You can find them in the wild on Routes 34, 35 and 47 in Johto as well as in the Cerulean Cave in Kanto.You can get a Ditto on Routes 34, 35, and 47. They can also be found in the Safari Zone and in Cerulean Cave on Pokemon HeartGold.
first you go to cerulean city gym. there is a team rocket grunt. he will run away. go farther into gym and run around where you find an inflate able tube. press "A" and you get the part.
at the cerulean cave
after you get all 18 badges and defeat the Pokemon league go to cerulian cav and mew two will be there