Elder brains are far from defenseless, but all the same they are useless in physical combat and prefer to allow illithids and servant creatures to fight for them. Elder brains can unleash the full arsenal of their psionic might on aggressors who threaten it, at twice the normal range. Anything capable of surviving this onslaught must deal with its defenders, and melee and ranged combat with the elder brain is inhibited by its submersion in the brine pool.
If the elder brain is aware that its massive psionic ability may be inadequate to stop intruders, it will grow brain golems in advance of combat. The elder brain needs sufficient warning for this, and this is a very rare occurrence. Despite all of these defenses, the elder brain has one last ditch ability if death is imminent. The elder brain can withdraw its mass entirely into the Astral Plane, permanently relinquishing its hold on the Material plane. Such rogue elder brains go on to an unknown fate, usually leaving their former community to quickly fall to pieces.
In addition to its psionics, the elder brain has a series of other innate mental powers. These mind powers all have a range of 2-5 miles, depending on the elder brain's age and size, and even work through solid rock.