In Final Fantasy Tactics Advance, the totema are the guardians of the crystals of Ivalice, which hold the world together. Altogether there are five, one for each of the races in FFT:A:
- Famfrit (who represents the Moogle race)
- Exodus (who represents the viera)
- Mateus (who represents the human race)
Each totema can only be summoned by its own race, and only after you have defeated that particular totema. Also, summoning a totema costs you 10 JPs so unless you're running around with an Action Replay or Gameshark hooked into your cartridge, they're something to deploy only in certain situations (i.e. against bosses, or other totema). Also, each totema does unique and massive damage: Famfrit, Adrammelech, and Mateus do HP damage, while Ultima and Exodus damage MP.
All of the totema are also from previous Square Enix games- Famfrit is the Dark Cloud from Final Fantasy III, Mateus is the corrupt emperor from Final Fantasy II, Ultima is the (same) fallen angel from Final Fantasy Tactics, Exodus is the evil tree mage from Final Fantasy V (also known as Exdeath or X-Death) and Adrammelech is a Zodiac Beast from Final Fantasy Tactics.
Sources:
Gamefaqs.com,
Official Final Fantasy Tactics Advance Strategy Guide,
and the game itself