This mantra is called the Shri Narasimha maha-mantra and it acts as a Kavacha mantra. So the people who chant this mantra is protected by the Lord Narasimha who is the most powerful avatar of Lord Vishnu.
Sri Nrisimha Maha-Mantra:
Ugram Viram Maha Vishnum Jvalantam Sarvato Mukham
Nrisimham Bhishanam Bhadram Mrityur Mrityum Namamy Aham
Sri Nrisimha Maha-Mantra:
Ugram Viram Maha Vishnum Jvalantam Sarvato Mukham
Nrisimham Bhishanam Bhadram Mrityur Mrityum Namamy Aham