I found some people being confused with a question, i.e. who was the 9th incarnation of lord Vishnu? Before I write anymore let me introduce Balaram.
Balaram was the son of Vasudev and Rohini. He was the step brother of Lord Krishna. Lord Krishna was the son of Vasudev and Devaki. Both Devaki and Rohini were the wives of Vasudev. Here you should not be confused; Lord Krishna is also called Vasudev.
As we know that Krishna was 8th incarnation of lord Vishnu. Balaram was elder than Krishna. How can Balaram be 9th? What comes first, 8th or 9th? Epics say that Balaram was the incarnation of Shesh Naag.