With Fire Emblem: Three Houses releasing later this month, Nintendo announced a promo for those who purchase the Switch game with a free Byleth: Tested Professor unit for Fire Emblem Heroes.
Basically you can get Byleth, the male protagonist of Three Houses, as a free unit by purchasing Fire Emblem: Three Houses either physically or digitally. All you need to do is have your Nintendo Account linked to both your Nintendo Switch system and Fire Emblem Heroes.
Starting version 3.7.0, which is slated to release around July 7, players will get to check their linked Nintendo Account emails under Misc. > Account Management. You can find more information here. The bonus will only be available to those who purchased the game and have earned Gold Points by June 29, 2020.
Nintendo also noted that the promotional unit Byleth: Tested Professor will appear in summoning events, with the first beginning in late July, so players who don’t plan on buying the Switch game won’t have to worry about missing out on an exclusive bonus. Those who do get it, will receive the Byleth unit starting July 26, 2019.
Fire Emblem: Three Houses releases for Nintendo Switch on July 26, 2019. Fire Emblem Heroes is available for iOS and Android.