Ok a lot of people still seem to have trouble getting this achievement… so for your sakes I’ll try to give you all a super simple explanation of how to attain it
If you want to do it the normal way, its easiest as previously mentioned to split the group up into the 4 corners and 1 in center for the barrage phases. Decide whose going where before hand and you should be able to outrun/dodge all the cannon blasts.
If you get hit or want to do the character swap method, I suggest you stay until all the cannon barrages have completed and your group actually kills Mai, yes kills her! Then you can go as far as to lower Horrik’s HP to almost dead before you switch characters.
You will need to have a group understanding of what you are doing so they don’t kill him before you return, as in running all the way back into the boss fight. While you are running back, your group will only need to evade his little cannon blasts until you enter the arena again, and yes you do need to re-enter the boss fight for the achievement to register. (I’d suggest hitting him a few times just to be safe)
Either method should render your achievement as completed so go get em kiddies!
Nice guide, but it doesn’t apply anymore. There is no way to enter arena after you switch characters. I tried it myself.. I run a whole way through the dungeon and no NPC or switch which could teleport you was present.