It is a wifi event and has past.
Celebi is the protector of the Ilex Forest.
You have to have a special (Wifi event) Pichu, bring it to the Ilex Forest Shrine. Otherwise, breed Pikachu/Raichu.
There is it is in ilex forest
A man in Ilex Forest
A man in Ilex forest will teach your Pokemon the move
Ilex Forest in not in Firered. Ilex Forest is located in Johto. It can only be reached in Gen II or in the unreleased Heartgold and SOulsilver in Gen. IV.
You must get the Pikachu-colored Pichu and transfer it to HG. You will get the Spiky-eared Pichu if you go to the Celebi Shrine in Ilex Forest.
Budew can be found in Ilex Forest and Viridian Forest.
Between Azalea Town and Goldenrod City.
A special event in ilex forest
There is a Move Tutor in Ilex Forest that teaches Headbutt.
there is a man in the Ilex Forest that will teach headbutt to as many Pokemon as you want