LogFAQs > #933051356

Here's some details from ResetEra:

https://bit.ly/36WSOfn

-Completely separate from the main game - you select it from the menu, select a Byleth/difficulty (no Maddening) and go.
-Takes place early in part 1. Byleth and the students pursue a mysterious figure and wind up in the Abyss, a town under Garreg Mach that the Church is silent on.
-The Ashen Wolves are former students of the Academy who have their own reasons for going to the Abyss.
-Doesn't follow the month/mission structure of the main game.
-No additional recruits - you have a set army.
-Said to be a little tougher than the main game.
-No word on if the characters will carry over into the main game upon completion, though the datamined supports/part 2 classes would suggest they would.

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Bart, with $10,000, we'd be millionaires! We could buy all kinds of useful things like...love! ~Homer J. Simpson