
Originally Posted by
Zohar_Lahar
Didn't Gekkai have access to a 4th "lost" mudra?
He did, and it comes up again later.
As of the 60-70 ninja quests, it turns out it's the norm for Hingan ninja to know about it. Doman ninja lack common knowledge of it due to them being wrongly viewed as outcasts/traitors by the former, which led to them severing ties.
I imagine it'll eventually be the next step in our progression, as they more thoroughly demonstrate the things it's capable of aside from the shadow clones Gekkai utilized.