"Mangalam Bhagwan Viro" is the beginning of a popular Jain mangal (auspicious) prayer or mangal shloka, recited at the start of religious activities and rituals. The full prayer is:

Mangalam Bhagwan Viro, Mangalam Gautama Prabhu, Mangalam Sthulibhadra-ādyā, Jaina Dharmostu Mangalam.

Meaning:

• Mangalam Bhagwan Viro: Auspiciousness be to Lord Mahavira (Vira here refers to Mahavira, the 24th Tirthankara).
• Mangalam Gautama Prabhu: Auspiciousness be to Gautama Swami, chief disciple of Mahavira.
• Mangalam Sthulibhadra-ādyā: Auspiciousness be to Sthulibhadra and other Acharyas.
• Jaina Dharmostu Mangalam: Auspiciousness be to Jain religion (Dharma).

This prayer invokes auspiciousness and blessings from the Tirthankara, chief disciples, Acharyas, and the Jain Dharma itself. It is recited by Jains at the beginning of their rituals, prayers, and important events.