Fire Emblem Echoes: Shadows of Valentia

Fire Emblem Echoes: Shadows of Valentia (ファイアーエムブレム エコーズ もうひとりの英雄王 Faiā Emuburemu Ekōzu: Mō Hitori no Eiyū-ō, lit. Fire Emblem Echoes: Another Hero King in Japan) is a Japanese tactical RPG game developed by Intelligent Systems and published by Nintendo for the Nintendo 3DS.

Functionality
Each figure unlocks a special dungeon where players can battle bosses and collect in-game items.

Players can save the current strength of Alm or Celica in the game to the corresponding amiibo figure.

During combat, players can sacrifice a portion of Alm or Celica’s health in order to summon a computer-controlled illusory hero that will act as a temporary ally for a single turn. Other amiibos from the Fire Emblem series, such as Lucina, can be used similarly to summon their avatars as allies for one turn phase. These summons will have a varied level based on the summoner's level.
 * Alm
 * Celica

Other amiibos used, (e.g. Archer Link), will summon at random additional phantom units, such as Barons, Sages or even enemy exclusive classes like the White Dragon, for one turn phase. For example, Mario summons 3 Mogalls on odd numbered turns and 3 Mages on even numbered turns. These summons all have the same level, so it is best to summon powerful classes over weak ones like Villager and Brigand.

A comprehensive list of non Fire Emblem amiibo summons can be found here.