use 18 sec invinsebility potions,
use first potion to get to the wall just straight to the right after you come in,
use second potion to get behind pandemonium (first boss) but step over the line so you don`t get agro,
use third potion to get behind the bubble,  there is a safe spot,
walk to the left near the wall and keep running untill you are behind the bubble, and abit to the right there is a safe spot, in the wall you running to,
now you are behind the bubble and that is the one you need to open,
cooldown of the potions are 10 min,
good luck