The Mara, sometimes called the Evil One, dwells in the dark places of the inside. Suffering is its delight, madness its meat and drink. It feeds off the fear generated when people look at it. Normally trapped in this other dimension, the Mara is able to cross over through the dream world. On the planet Deva Loka, it uses the Kinda's dreaming chimes to ensnare people who dream alone. To those dreaming, the Mara shows itself in the form of people wearing antiquated clothing, each bearing the mark of a snake on their right arm. The Mara tries to drive the dreamer insane in order to force them to allow the Mara to borrow their form - it promises them that they will be entertained by the experience. Once they consent, the Mara can take them over in both the dream and real world. And even if banished from the real world, the Mara can exist as a latent mental force in the dreamer's mind, using their dreams to increase its power. Its mind-control abilities also seem to extend, to a limited degree, to those who agree to help it. In the same way as agreeing to play host to the Mara gives it complete control over a person's body, agreeing to do what it asks gives it some control over a person's mind. It may also appear as a snake's skull, reflected in glass or mirrors.
People possessed by the Mara have red-rimmed eyes, bright red lips, and their teeth are stained red as though their gums have been bleeding. Their entire face may turn red, and even their eyes may briefly glow red. They are characterized by a certain evil glee, particularly concerning the fear, pain and suffering of others. Those possessed by the Mara seem to be continually amused by the fear they engender, and laugh wickedly at such spectacles. However, if the possessed person has a strong enough personality, they may be able to keep from changing totally. (Alternatively, it could be that the Mara allows the change to happen gradually if it needs to allay suspicions.)
On their right arm is the mark of the snake. The Mara can transfer itself from person to person - when this happens, in either the dream or real world, the one possessed links the fingers of his right hand with those of the person to whom the Mara is being transferred. Once this is accomplished, the snake mark comes alive and crawls across the linked hands to settle on the forearm of the other person - a process that is apparently either painful or terrifying, as the recipient usually lets out a tortured scream. The mark of the snake can serve as an identification to open secret doors placed by the Mara, and if the Mara has absorbed enough energy, the mark can also rise off a person's arm and become corporeal, even down to the venom dripping from its fangs.
As evil cannot look upon itself, the Mara cannot bear the sight of its own reflection. If the Mara is surrounded by a circle of mirrors, reflections of reflections that it cannot escape, it will retreat. The Mara will detach itself from its host in the form of the snake mark. The snake then grows to quite gargantuan sizes. In its true form - a large snake - the Mara looks almost unrealistic, rather like a large rubber snake. If still surrounded by the mirrors, without a gap through which it can escape, the Mara will then vanish back into the dark places of the inside. Presumably once it has left a world, it can never return.
The Mara originated on Manussa, planet G139901KB in the Scrampus system and former homeworld to both the Manussan and Sumaran Empires. The Manussan Empire was a technologically advanced society which suddenly suffered a cultural catastrophe and disappeared. The Sumarans, as recorded by the Federation when they came to Manussa six hundred years later, were a primitive people enslaved to the Mara. One hundred years after this encounter, the Federation destroyed the Mara - or so they thought. In fact, they had only banished it to the dark places of the inside. Legends of the Mara's return flourished on Manussa, saying that it would return in a dream to regain its power over men when the minds meet again in the Great Crystal.
Also known as the Great Mind's Eye, the large, blue Great Crystal and several smaller, pentagonal blue crystals like it were manufactured eight hundred years prior to the Doctor's visit to Manussa in a zero-gravity environment, ensuring that they were flawless and perfectly tuned to the exact wavelengths of the human mind. The crystals had the power to transform thought into energy, and when the Manussans used the Great Crystal, it absorbed what was in their minds. The nature of the energy it absorbed determined the nature of the matter created: in this case, it absorbed, amplified and reflected their restlessness, hatred and greed, and created the Mara.
The smaller crystals act like a radio wave, transmitting thoughts between those wearing them. When in use, they emit a harmonious high-pitched sound. This function is particularly utilized by the Snakedancers, a group of people devoted to serious study of the Mara. They live in the hills, subsiding on roots and berries, where they perform ceremonies that involve them being covered in ash, almost naked, going into trances and handling live snakes. The Snakedance is a dance of purification, to clear the mind, for they believe that only those with clear minds can stop the Mara by finding the still point within themselves. Dojjen, a prominent Snakedancer, had this to say about where the Mara existed: "Where the winds of restlessness blow, where the fires of greed burn, where hatred chills the blood, here in the Great Mind's Eye, here in the depths of the human heart, here is the Mara."
As the Great Crystal was, thus, the source of the Mara's power, it planned to use it to reform itself on Manussa. It manipulated Tegan into setting the TARDIS controls for Manussa, during one of the celebrations of the Mara's defeat that took place every ten years. Once it obtained the Great Crystal, it inserted it into a special slot in the mouth of a carved representation of itself. The Crystal then absorbed the mental energy and belief of the people gathered for the celebration, giving the Mara the power to manifest itself and grow larger. It required all the minds present to look at it, believe in it and submit to it; but the Doctor was able to find the still point, disturbing the flow of the energy and halting the Mara's Becoming. He used one of the small blue crystals which, with Dojjen's help, burned the hands of those possessed by the Mara when they tried to take it from him. This enabled the Doctor to reach the Great Crystal in its socket, and remove it. The Mara's link to Tegan was severed, and the snake collapsed and died in a pool of pink ichor. Finally, the Mara was truly dead.
