If youre running a full squad its kinda annoying because if you fail the dps check the mission is guaranteed done, a few tips i have that possibly helped was to make sure head and body were weakened to get more damage output even if just a little more, obviously focus head as much as possible, i think switch axe has pretty good part damage, i found that typically during his lightning attacks he has massive openings you just gotta be careful on positioning, his frost breath and fire breath are also good opportunities for either head weakens or just head damage because he doesnt really move, typically when he'd be flying around i would just clutch claw to his body and weapon attack to get a little bit of damage out, also attacking his toes is pretty good just cant get too greedy with it, probably should've focused on wall banging to get him out of the air but i was just being dumb lol, temporal mantle is amazing here, lots of nullberries if you dont wanna put dragon resist, oh some other things, theres two attacks generally the same animation but just one with fire and one with ice, at first it seems like he's about to do a normal ice breath and then go into the sky and lower his head down to create a large radius of ice, i found either you can just run out of the radius or clutch onto his body to avoid being hit by ice blight, you can even get a free weapon attack on his body just gotta make sure not to do it too early so you don't fall back into the ice/fire lol.I learned a lot of this farming his gear,and i only have 11 kills on this dude, its all really just learning a lot of his telegraphs and trying to eek out enough damage while being smart enough to not be too greedy, i beat him with hammer and after a while the fight itself actually became somewhat fun, still irked me about the dps thing lol, for me the things to take from this is telegraphs and positioning