This article compiles a summary of the Fire Emblem Echoes: Shadows of Valentia available Amiibo including their effects when linked to the game .
Past Heroes as Ghost Soldiers
When pairing a FE character Amiibo for this game, it allows you to summon a hero from the previous installment as a Ghost Soldier. Although you do not have control over these characters, they function as NPCs in the game.
Special Dungeon Access
Another feature that is only accessible via the Amiibo pairing is the Special Dungeon. By linking the Special Alm and Celica Amiibo to Fire Emblem Echoes, you will unlock this dungeon. This will consequently send you Ghost Soldiers of Alm and Celica which retain their stats based on your previously saved data.