You only need 1 spell (PrC)

[Fax Celestis]

That's kind against the point.

Fireballers normally are spellcasters. They are usually warriors, fighters, barabarians, rogues, and other nonprimary casting classes. Fireballers are taught only one spell: Fireball. They cast it a lot. A WHOLE LOT. They skipped learning know to cast spells and how to modify spells. Fireballers are often the "I don't speak English" of the magic world.

"Yo no hablo ingles. YO HABLO BURNINATION Y FIERY APOCALYPSE FROM THE SKY. BWAHAHAHAHHAHAHAHHAAHAHAAHAAAAAAAAAAAAAAA!"