By Level Up:
* Gengar: Learns Shadow Ball at level 44.
* Houndoom: Learns Shadow Ball at level 49.
* Absol: Learns Shadow Ball at level 49.
* Spiritomb: Learns Shadow Ball at level 59.
By TM:
* Any Pokemon that can learn Ghost-type moves can learn Shadow Ball by using TM30.
By Breeding:
* Eevee: Can learn Shadow Ball by breeding with a parent that knows it.
* Murkrow: Can learn Shadow Ball by breeding with a parent that knows it.
Note:
* Some Pokemon may require an evolution or specific held items to learn Shadow Ball.
* The level at which a Pokemon can learn Shadow Ball may vary depending on its evolution stage.
This information should help you find the perfect Pokemon for your FireRed team that can learn Shadow Ball!