Shri Krishna became daughter in law of Arjuna

Sounds strange, but this is for real. This too was done for ensuring victory to Pandavas. Arjuna’s son Iravan sacrificed himself before Kurukshetra war.

Iravan, was the son of Arjuna from princess Uloopi. Before the start of the Mahabharata war, he agreed to be sacrificed to Goddess Kali to ensure victory for Pandavas. But he had a wish to be married before he died and this created a problem.
There was no girl who would be willingly married to a person who was about to die. Enter Shri Krishna. He became Mohini and married Iravan thus fulfilling his last wish. Not only this, after the death of Iravan, Mohini wept and was sorrowful like a widow.

Unknown stories on Arjuna 

Shri Krishna as a wife to Iravan - Arjuna' son
Shri Krishna as a wife to Iravan – Arjuna’ son