Disc One Final Dungeon

[Sephiroth]

Final Fantasy IV:

1. After Golbez flying fortress/tower
2. After the Tower of Babil
3. Theodore is awoken
4. Moon, Lunar Subterraine

Final Fantasy V:

1. Right before entering the otherworld (so the whole crystal and meteor thing being the final dungeon)
2. X-Death's Castle
3. After getting the books, so the last dungeon of them
4. The Rift

Final Fantasy VI:

1. Narshe or Zozo, Terra flies away or finding Terra or wake up Terra (Terra)
2. Floating Continent, Kefka activates the statues and everything is about to be devastated (Kefka)
3. Mobliz, Terra joining (Terra)
4. Kefka's Junktower (Kefka)

Not always classical a dungeon but an important plot moment.