How to Recruit Lizzie - Dragon Quest 6
Lizzie is one of the two optional party members available that isn't a Slime. You can recruit Lizzie to your party at any point in the game after recruiting Terry and obtaining the Ultimate Key. Head on over to Arkbolt and up to the outside balcony that goes to the throne room. You'll find a set of stairs in the southeast of this area that lead to Lizzie.
If you have the Ultimate Key you'll be able to open the cell door and speak with Lizzie. Without Terry in your party Lizzie won't talk to your group but with Terry she asks if she can join you. That's all there is to recruiting her!
Note: She is not available in the SNES (original release) of the game; only in the DS and Mobile remakes are you able to recruit him to your party.
Out of all the optional characters in the game, Lizzie is by far the strongest.
Vocation Permanent Rewards
These are the passive & permanent rewards that you will get when mastering a Vocation. You'll keep these boosts even when switching to a different Vocation. Once you reach level 5 in every Vocation you'll receive a Gospel Ring from the priest in Alltrades Abbey as well which will allow you to avoid encounters. You do not need to reach level 5 in every Vocation on 1 character, it can be done on multiple characters.
Gladiator: +20 Strength
Armamentalist: +20 MP
Paladin: +20 HP
Sage: +20 MP
Ranger: +20 Agility
Luminary: +15 Style (or 20)
Hero: +40 MP
Dragon: +20 Strength
Liquid Metal Slime: +100 HP