He is in the one island Pokemon center he's the guy with the glasses near the big machine.
celio is on the first island you can go there after you win at the cinabar gym, bill will be wating for you outside the gym
Hes bills friend on island 1
You find the ruby and give it to celio
there is no cecilio,,, celio only,,, you can find him in the johto region,,,
You also find the sapphire and give them both to Celio.
beat the elite four
Celio is the man standing right by the giant machine in the One Island Pokemon Center you can't miss him.
When you beat the elite 4 and find the ruby and Sapphire for Celio!
to get to ruin valley on Pokemon leafgreen you have to get the ruby in mt. Ember and bring it back to celio then go to six island
you find him on one island in a building with a pokeball on it and a red roof.
On five island you need to have given the ruby to celio to get there.
He is on 1 island in the Pokemon center building in front of the huge machine