i don't know how to get celibee but u get mew by doing the mew glitch in red,blue or yellow and the trading it to leaf green or fire red
if u know the mew glitch don't read this part
things u need
Abra, to not have killed the guy left of nugget bridge , to noy have killed the guy to the east with a lvl 17 slowpoke and alot of pokeballs
i recemend u save b4 u do this
so the way to do this is go to the water near the nugget bridge and walk 1 step forward so the u can see grass and water but if u take 1 step down the guy left of the nugget bridge will fight u if he does turn off then back on cuz u stuffed up instead of fighting him u take 1 step down then instantly press start after that u use Abra and teleport to the town just below u if u do this right u will not be able to acces the start button screen. once u have teleported you go to the guys with slowpoke and kill him then teleport again but this time half way up the bridge ur start button will open press "b" and u will be in a fight with mew
The only problem with that is that you cant trade Red, yellow or Blue to Fire Red or Leaf Green, but if this works on leaf green or fire red, then that's ow you get mew.
Now, to get celebi, you must finish the game, 'Pokémon Colosseum' on the Nintendo gamecube. this means, catching all the shadow pokemaon and purifying them and reaching to lv 100 of the Tower. then, eagus will take you to the place where you purify the pojemon, and celebi will come down and eagus will tell you something along the lines of, "Celebi has seen how well you are with taking care of Pokemon, so he wishes to join you on your adventures" that's not exactly what he says, but close enough.