It's the second boss in the green section. For what it's worth, I think that fight is an ill-conceived pile of garbage, because the boss constantly changes color and you barely get any damage in. Feels like a fight designed for a group - the kind that stops you from soloing a dungeon or world boss not because it can't be done, but because it's just so tedious. I got Flawless on vMA by the way - a place I quite enjoy.
Part of this may be due to being a PvPer. I will never get the highest scores in vMA, because I don't have the DPS nor am I interested in honing that. These days I go to test out my latest PvP builds, usually with only minor changes, against something consistent. As I play light / medium, fairly high damage characters, that works. I typically get a vMA score in the 400K to 450K range.
This fight seems to be designed for laying down ground DOTs in advance and doing as much DPS as possible, the kind of thing true endgame PvEers do. At the same time, as Alcast says, it's also a stamina-intensive fight, which actually suits PvP-derived builds. It's a pain in the behind for both types of players, the squishy high-damage PvEer and the somewhat tankier PvPer who brings some stamina sustain, even on a magicka build. At any rate, if you don't bring the damage, the fight is interminable. I hate how high-end content tends to be a DPS race. This is not a DPS check as such, but the longer the fight goes on, the more likely you slip up from sheer boredom.
Edited by fred4 on November 24, 2020 2:07AM PC EU (EP): Magicka NB (main), Stamina NB, Stamina DK, Stamina Sorcerer, Magicka Warden, Magicka Templar, Stamina Templar
PC NA (EP): Magicka NB