In past Fire Emblem games character customization was limited to only certain aspects of your units: you could customize the skill setup to make the best out of each units’ traits but there was no way to completely change class: the only class change feature was the possibility to evolve into some advanced forms of the same class, granting higher stats but not different abilities during battle. Fire Emblem: Awakening is the first game of the series to offer the possibility to switch classes by using the Second Seal, allowing characters to switch to another class which is not too different from their starting one. Together with the Second Seal, the Master Seal makes a comeback, allowing units to switch to an advanced form of their class.
- Master Seal
Like in previous Fire Emblem games, the Master Seal allow characters to improve their class once they reach level 10. Using it as soon as a unit reaches level 10, however, is simply a poor decision: the units’ level cap is 20 and while the advanced forms have overall better stats than the basic class, you will be loosing some good stats if you decided to advance before reaching the cap. This strategy will make the advanced unit even more powerful: coupled with another trick involving the Second Seal you may be able to create some incredibly powerful units.
- Second Seal
The Second Seal allow characters to completely change their class into another basic class. Please note that the available classe for choosing will be limited, depending on the character: there’s no way for a Warrior to become a Wizard or a Priest and there’s no way for a Wizard to become a Berserker. Also note that classes available after using the Second Seal will all be starter classes with no real advantage on each other stats wise. Using the Second Seal allows players to finally have more customization options: you can also use the Second Seal to grind and have powerful characters at your disposal. Using the Second Seal will make the unit go back to level 1, starting however with some stat bonuses. You can reset the level a couple times after reaching the level cap to create some powerful units: morph them into advanced classes with the Master Seal to take even more advantage of this simple trick.
Article from Gamersyndrome.com