I did near 150 runs in s25 and it didn’t spawn once. Previously, on many attempts, it has spawned consistently between 30 and 40 runs for me. I have found this dungeon around 10 or so times over the past 6 years. I like finding things, so sometimes, I just get silly and do these farming runs over and over just for the fun of the dungeon spawning. I already have the xmogs (I have all of the xmogs, including the Blues).
It is low, from my experiences 2.5-3%.
1% is way too low based on my extensive experiences.
Yes, can 100% confirm that it spawns in adventure mode. I think MC is thinking of Griswald’s edge (sword) which ONLY spawns in campaign mode. That’s around 1/1000 chance of dropping (still not as rare as Wirt’s leg).
I could do more runs to test my theory, but I do suspect that it has been removed from the game. I wondered about this, but never posted about it.