Drain Life with the Stagger node is capable of permanently stunning everything that isn’t stun-immune. Based on some answers on Discord, I believe this is a bug and it is supposed to only be able to apply once per mob, however it can currently be applied repeatedly.
The long description of what exactly happens:
Drain Life has a passive called Stagger, which applies a guaranteed 2 second stun after channeling on an enemy for 3 seconds continuously.
The following node, Stupefy, increases that stun to 4 seconds.
Channel Drain Life until you see the Contempt buff pop up on your bar (lets you know exactly when Stagger has triggered).
Stop channeling and go to step 3 until the monster is dead.
Enemies seem to be capable of activating instant cast abilities every time you reapply the stun, which makes it hard to pin down some bosses like Rahyeh or Julra, but some bosses are made completely trivial with this, like Heorot who is unable to even activate his add phases.
I did see issues like that in my searches before posting, but I want to be clear that this is a different problem. I do not experience it bugging out any enemies’ AI (probably because Lagon is now immune to stun).
The specific bug that I was reporting here is the ability to repeatedly apply Drain Life’s guaranteed stun to the same target.
That said, when someone claimed on Discord that Mike answered it can only apply once to each target, I never found his actual response. Just went and found it this time, and really from context it looks like Mike just meant once per target per channel. So, in the end I’m not sure this is a bug (since the skill/passive never mentions anything about a limit), but it definitely needs to be addressed eventually. I’ll try bringing it up again on Discord.