Read this post about an introduction to the Rasas.
After escaping from the devious designs of Duryodhana to burn the Pandavas alive in the house of lac, the brothers entered into a forest which was the domain of an asura called Hidimba.
Given that the Pandavas were very tired, they went to sleep with Bhima standing guard over them. When Hidimba smelt the humans, he was excited as it had been quite a while since he had humans for food. He called his sister Hidimbi and asked her to lure the humans into her trap and lead them to her. Bidding to do her brother’s instructions, Hidimbi used her asura powers and transformed herself into a beautiful woman and set out to lure the Pandavas into her trap. However, when she laid her eyes on Bhima, she immediately fell in love with him.
She approached him and tried seducing him with her looks to no avail. Bhima was so uninterested that he initially didn’t even want to have a conversation with her. However, when Hidimbi revealed the true purpose of her approaching Bhima and also told him as to how her brother HIdimba planned to kill and eat him, his brothers and his mother, this enraged Bhima.
In the meantime, irritated by his sister’s delay in bringing the humans to him, Hidimba himself approached the Pandavas. When he saw Bhima and Hidimbi engaged in conversation, Hidimba was besides himself with anger. He willed himself to assume his most demoniac form using his formidable asura powers and attacked Bhima. By some accounts, in this form, he was more than 12 ft tall and reasonably wide as well making for an extremely scary sight for any normal human being.
In the fierce battle that ensued, Bhima managed to kill Hidimba and save himself and his family from his clutches. He then went on to marry Hidimbi who gave birth to Ghatotkacha as a result of their union.
Thus, the bhayanaka rasa finds mention in the Mahabharata in the asura form of Hidimba who was slain by Bhima.