Ravana was known for his ten heads and was therefore known as Dashanan. It could be that his mental power was ten times that of a normal human being.
Experts who study Hindu shastras say, Ravana used to create the illusion of ten heads.
In reality, he was single-headed, but in acts of deception, he used to fool his enemies by creating an illusion of having ten heads.
The Ramayana says, Ravana went to battle with Lord Rama on krishna paksha amavasya (New Moon) and during the battle, he used to lose one head every day.
On the dashami, celebrated as Vijayadashami, he lost his tenth and last head.
The rakshasas (demons), according to Ram Charit Manas, were masters of illusion. Take the example of the demon Maarich, who created an illusion of a golden deer, silver star spangled and all, and drew Rama away from his wife Sita.
Or, Ravana who created the illusion of producing the severed head of Rama in front of Sita to deceive her.
It was this Indrajaal, the black art of illusion, that created ten heads and twenty hands for Ravana.
Some Jain religious works reveal, Ravana had a necklace of nine big gems, which reflected his nine heads.