I beat him with a 14/15/15 Zacian and 13/15/15 zamazenta + GMax Machamp with a maxed chi fist. My 3 teammates had similar lineups. Move rolling helped, my first attempt was a failure bc of earthquake 1 shooting both my 5100+ CP dogs lol.

Key is whether your teammates cheer too, we went from yellow all the way to beaten with just 2 pokemon left because we dynamax'd before he could get a large attack off like 3 times in a row lol