waterfall
you need to use the HM waterful you get from a girl called jasmine in sunyshore first defeat the gym
You have to get the HM Waterfall, which can be obtained in Sunyshore city after beating the last gym.
from that gym leader on the beach of sunyshore city (must have beaten the 8th gym)
In sunyshore city there is a woman sitting on the sand at the north part of the city who will give it to you but you cant use it until you have the sunyshore city gym badge.
from jasmine in sunyshore beach if you defeated the eighth gym already.
The 6th gym (Steel type) does not unlock any new HM , instead the 16th Gym (Blue's Gym) unlocks Rock Climb
After defeating 8th gym, go talk to Jasmine on the beach of sunyshore and she will give it you
You obtain the HM from Jasmine once you have won at the Gym in Sunyshore.
in sunyshore city, after you beat the gym leader,(no.8)talk to Jasmine(girl on the beach) shell give the HM 08. (Waterfall)
No. The last HM is in Sunyshore. Anyway, you have to beat/catch Dialga/Palkia to get to Sunyshore City.
Talk to Jasmine (Steel type gym leader in Johto) who is on the beach in Sunyshore city, she will give you the HM waterfall which you can use after you get the gym badge in that city, you can use it to get to the Pokémon league. (Aaron (bug) Bertha (Ground) Flint (Fire) Lucian (Psychic) and Cynthia (All-rounder))
the actual HM the leader doesn't give to you, but it is located on a route near Sunyshore, home of the final gym leader, who allows you to use waterfall. this is for Pokemon diamond, pearl, and platinum.