This achievement comes after finishing dungeon boss level 60. You will need to fend off the indirect attacks from Goliad and Stormo's psychic assault for 120 seconds.
DO NOT ATTACK, YOU CANNOT DAMAGE THIS BOSS
The point of this battle is to stay alive.
First, they will start with either a ring of fire, in which you need to dodge, or a spray of red ball attacks, which you also need to dodge. After this, normal enemies may appear to try and distract you, try to stay away from them, only kill them if you must.
The next attack will be twisting lightning bolts. There is no real easy way to dodge these, but using the corners to hide seems to work well. While this is happening be sure to look-out for falling rocks as well as picking up any health that may drop from killed enemies.