Together We Stand

[spell=243963] is triggered whenever a player is not within 8 yards of another player. To deal with this mechanic have your raid stack up near a wall.

From there simply pull Varimathras, nuke him and you'll get the achievement.

This does appear to be soloable, IF you can kill him before the first cast of alone in the darkness. I killed him in 12ish seconds and got the achievement, so do your max burst and kill him ASAP!

The simplest solution to deal with the knockback is to have the raid position with their back to the corners. Either the upper right, or upper left corners of the room will work as the corners are spaced far enough apart for dark fissure. Place down 4 raid markers spacing out. as a movement reference point.so the tanks, melee and range stay within the 8 yards required for the achievement.