Squad Assault

Squad Assault is a very difficult game mode from Fire Emblem Heroes where Heroes will be captured by the enemy after completing a map. Once captured, they cannot be deployed again until the challenge ends. Clearing this mode will earn you Sacred Seals and Orbs.

Basics
After clearing one map, you'll immediately continue to the next map. Heroes who participate in battle are captured after one map and cannot be used again.

Each map requires four Heroes and you must have enough Heroes to complete all maps in a set. For example, for five battles, you will need 20 unique Heroes. Also, you are not allowed to use duplicates of a Hero, meaning if you used an Olivia in the first map, you cannot use another Olivia in the following maps. Upon clearing a set of maps or losing, all Heroes will be released. This means that all your Heroes will be free to battle once again.