Five times.
1. Tellah fights Golbez in the Tower of Zot.
2. The party fights Golbez in the Dwarven Castle.
3. FuSoYa and Golbez fight Zemus.
4. FuSoYa and Golbez attack Zeromus, and get annihilated.
5. Golbez and FuSoYa appear on the battle screen to provide Cecil with health before the final battle.
If that is correct, then what happens if you try to re-enter the Tower of Babil through the Cave in Eblan?