It's the one where you neutralize or stop Vana from spawning slags. I've been told that you had to count to 3 misissippis starting from the time Vana stands still in the center before he respawns the zombies. I've gotten to work a couple of times, but I've actually counted up to 4 or 4 missis.... and then threw. Other times that it seemed to have worked it seemed like my party members who attacked at the right time activated the glitch. On the other hand, I think I've seen my team members just hold up a vial glitch before the 1st phase where you're locked around the square fire tiles. Other times I've seen it thrown with/without success.
I've never seen any youtube video or topic search on this, so help would be appreciated, thanks.
I wish you luck on the upcoming patch.