Ghatotkacha Parva is the seventieth Upa parva included in the seventh Maha parva named Drona parva. Vaishampayana continued narration to Janamejaya in reply to his queries as follows.
Duryodhana had requested Drona to kill the demon Ghatotkacha. How and when was it done, and by whom?
After becoming the commander in chief of the Duryodhana army, on the fourteenth day night, Karna had killed Ghatotkacha. But it was a pending order of Drona to Karna so this narration is included in Drona parva.
Who was Ghatotkacha and when did he join the Pandava army?
Ghatotkacha was the son of Hidimbi and Bhima. He was a demon. His style of war was suited to demons. Ghatotkacha’s references are already mentioned on this website under various parvas like Mrigaswapnodbhava parva, Jatasuravadha parva, Ajagara parva, Amshavatarana parva and Hidimba parva. As soon as the Mahabharata war was declared, Ghatotkacha had started to Kurukshetra and on the ninth day, he had joined his father in the war. On the same day, Drona became more active in keeping Ghatotkacha under control, so this parva is also included under Drona parva.
Since he was a demon, to fight him, Drona recruited many demons into his army. But Drona died first on the thirteenth day night and later on the fourteenth night, Ghatotkacha was killed by Karna when Karna used his preserved Vasavi Astra. Initially, Duryodhana had attacked Ghatotkacha but Duryodhana was defeated by him so Duryodhana had escaped from the battlefield directing Karna to kill him. Later Duryodhana was very happy when Karna had successfully killed Ghatotkacha.