Sorry for the long essay, but you will thank me afterwards.
I finally have the best and flawless way of getting past this dungeon without touching the lava. Hopefuly so that many more can now get this without any issues.
You die before you touch any lava and simply run across. It was mentioned in the other guide, but this time I got an even better way.
Best used on a damage dealer or healer as the tank needs to stay alive for the 4th boss on those platforms.
As a "dd" or "h" use a skill that drains your health such as equilibrium in the mages guild, then simply equip the "potion" (not poison) called ravaging health and instakill yourself.
Right before any lava once your through the door (after first 2 bosses) use this and slowly reach the next solid platform and repeat (some you can do in one run, near the beginning) and some you can stop halfway.
Lastly, on the 4th boss, cause as much damage as you can on the boss. Wait for him to do his aoe mechanic and suicide on the left, so that another dd or healer can revive you after the mechanic is over. The other two players including tank keep the boss busy. Rice and repeat. Once dead, suicide and run across the lava to the final door. Same again, suicide across the final part.
As for the final boss, lava does not void the achievement, just don't be silly and run to one of the two corners with static lava and jump in it.
Achievement unlocked. Did this 4 times as I helped everyone in the group get it too.
Best tips:-
You can do this on your own, no group achievement
Better with dd or h, as tank needs to stay alive
WATCH OUT FOR SPALKS TARGETTING YOU
(If your near lava, there lava bomb and push you into the lava) Spalk target does not void this.
Final boss lava that spawns, does not void this
You HAVE TO kill all the adds in this dungeon, DO NOT skip, as the achievement says all of the attendants.
(Skipped first adds, had no achievement)