Tank in Leviathan EX

[Atreides]

Dreadwash is not unstunnable per se.
The add just happens to build a stun resistence really quick while not stunned, after a while he just becomes immune to it which it usually is by the time it casts Dreadwash.
We usually stunlock it and never have trouble. We start it like 5 seconds after it spawns, then just stun again 2 secs after it wears off, by the time the 3rd is done the add dies without getting anything off.
If something goes wrong you can always have a summoner or white mage knock the add away to interrupt his cast.
I'm well above 70 kills now and so far it always worked. The mirror has yet to drop...