Hey, (Spoiler alert.)
You can't kill/destroy it. Just grab the Acorn, open the door via the console next to a broken window
and then run. The void creatures are invincible, but they die like the doppelgangers after a few turns. I recommend to use the expert sprint und the temp. ability that gives you extra mps and aps. + you should also carry a low
Penalty armor and some striders or tabiboots for the maximum ammount of mps. You could just ignore it but then you need a lotta health hypos. If you play on hard or higher, you should follow my suggestions.
If you focus your mind on the monlith before dou grab th Acorn you get a pretty good
psi related first.
-Azura