Final Fantasy Tactics A2: Grimoire of the Rift/Secret Characters

Frimelda
By following a chain of quests starting with "Under the Weather" (B4-07) and ending with "The Way of the Sword" (B5-11) the female paladin turned zombie will join your group. She looks and acts as a Hume (can go into any Hume class) and comes with some basic paladin action abilities and the Dual wield passive ability.

Monteblanc
You need to be post-game (GAME COMPLETE file) and need three things:
 * 1) Giga's Pendant (quest: "Camoa Cup")
 * 2) Pin of Order (quest: "Fluorgis Cup")
 * 3) Earrings of the Dead (quest: "The Last Step")

Then, there should be a mission available called "Wanted: Friends, Kupo". Do it, then you will unlock the moogle montebanc, who is a black mage class. He knows the full black magic set.

Al-Cid
Al-Cid can only be unlocked after the game has been completed. Then there should be a mission called "A Refined Recruit", and Al-cid will join your party. Al-Cid is a hume Agent, and can only learn Reconnaissance.

Penelo
Penelo can be unlocked before or after the game is completed. After loading up the completed save game file, travel to fluorgis there should be a mission called "An Elegant Encounter" where Al-Cid give you a letter to give to vaan and penelo when Al-Cid leaves penelo will arrive asking if you have seen vaan at this point she will agree to accompany you in finding vaan. Penelo is a hume but is treated by the game as a viera for the purpose of laws and uses viera jobs with the additional unique job of Dancer.

Vaan
To unlock vaan complete the mission "An Elegant Encounter" after leaving the aerodrome head to the event bubble in 'Cannol West Barbican' to start the mission "where could he be" where you will have to do battle against 2+wolfs 1+Gladiator 1+ Berserker 1+ Beastmaster  while keeping vann who is immobilized alive take a balanced party and you should have no trouble after the battle is won Luso gives vaan the letter Al-Cid asked him to deliver vaan and penelo will explain a bit about what has happened since the last you last uncounted them and vaan will be available to join