She immediately transformed into a beautiful maiden. Gone were her ugly looks and hunched back. Kubja shyly looked at Krishna with her pretty eyes, and invited him to her house.
Krishna accepted her invitation saying, "My dear beautiful girl, I will surely visit you when I have finished with the business that I have come to Mathura for."
The sacrifice that was arranged by Kamsa was called Dhanur yajna.
Krishna asked the people where the sacrifice was to be held and they pointed to a decorated arena, where in mid center a huge bow was present. The guards did not allow him near it, but Krishna magically got past them, heading towards the bow.
He picked it up and broke it into two with no effort at all, and killed all the soldiers who were attacking them.
Kamsa consequently sent more soldiers to attack Krishna, but all of them were killed.