On 1 Island, he's standing next to the trading machine inside of the Pokemon center.
find the ruby and give it to celio.
Find the Ruby inside Mt ember and then give it to Celio.
If you mean Celio, his in one island pokemon center.
one island
give it to celio
if u havent then you could catch mewtwo, or nothing at all or whatever u wish
Deliver it to celio and now you can trade with sapphire or ruby version. To trade with emerald you need two wireless adapters. Also after that finish the pokedex oh and try the trainer tower.
You give it to Celio
on island 1, in the pokecenter. u can get to island 1 by acheiving the rainbow pass
While it was possible to find missingno. in Red version, it is not possible to find it in FireRed.
he is in one island in the hospital.
Give it to Celio on one island.