I read somewhere that a heroic warrior killed in the Mahabharata war was revived for one night. Is it true? Who was he?
Yes, the dead were revived for one night.
Vaisampayana said, 'When night came, all these persons, having finished their evening rites, approached Vyasa. Dhritarashtra of righteous soul, with purified body and mind solely directed towards it, sat there with the Pandavas and the Rishis in his company. The ladies of the royal household sat with Gandhari in a secluded spot. All the citizens and the inhabitants of the provinces ranged themselves, according to their years. Then the great ascetic, Vyasa, of mighty energy, bathing in the sacred waters of the Bhagirathi, summoned all the deceased warriors, viz., those that had fought on the side of the Pandavas, those that had fought for the Kauravas, including highly blessed kings belonging to diverse realms. At this, O Janamejaya, a deafening uproar was heard to arise from within the waters, resembling that which had formerly been heard of the forces of Kurus and the Pandavas. Then those kings, headed by Bhishma and Drona, with all their troops, arose by thousands from the waters of Bhagirathi. There were Virata and Drupada, with their sons and forces. There were the sons of Draupadi and the son of Subhadra, with the Rakshasa Ghatotkacha. There were Karna and Duryodhana, and the mighty car-warrior Sakuni, and other children, endued with great strength, of Dhritarashtra, headed by Dussasana. There were the son of Jarasandha, and Bhagadatta and Jalasandha of great energy, and Bhurisravas, and Sala, and Salya, and Vrishasena with his younger brother. ........ These and many others, who for their number cannot be conveniently named, appeared on that occasion. All of them rose from the waters of Bhagirathi, with resplendent bodies. Those kings appeared each clad in that dress and equipt with that standard and that vehicle which he had while fighting on the field. All of them were now robed in celestial vestments and all had brilliant ear-rings. They were free from all animosity and pride, and divested of wrath and jealousy. .... At that time, through the puissance of his penances, the great ascetic, the son of Satyavati, gratified with Dhritarashtra, gave him celestial vision. Endued with celestial knowledge and strength, Gandhari of great fame saw all her children as also all that had been slain in battle.....'
Mahabharata, Asramavasika Parva Section XXXII