Far from the quarrels of the other houses, the group of outcasts who formed the Ashen Wolves in Fire Emblem Three Houses resides in the Abyss under the monastery. They have to face yet unknown invaders until Byleth and her band land with the Expansion. You won't be able to choose this new house during the main campaign, it's exclusive to a separate game mode with its own savegame. But be reassured, you will still have the opportunity to recruit the new students in the campaign once the DLC is completed for the first time.
Ashen Wolves
This house has only 4 students instead of 8, and they live in a devastated area under the monastery, called the Abyss. It seems that this house is exclusively composed of fallen nobles from the 3 main nations, and they all have a certain predisposition to magic. This makes them versatile and quite fearsome characters considering their statistics. As part of the secondary story, they will all have access to a new special class.
Ashen Wolves members
This class would have been created following the proposal of Alphard, who, although he does not serve as a teacher, seems make the link with the monastery and the Church of Seiros.