While we see direct participation of Narayan in Mahabharata, we also witness the presence of Mahadeva throughout the proceedings that culminated in destroying adharma from the root level.
Shiva is in the form of Vishnu and Vishnu is in the form of Shiva. There is no difference between them and both provide Auspiciousness. Hence the Epic Mahabharata got Krishna as well as Shiva dictate the proceedings towards establishing dharma in Dwapar yug.