Can I get the new form of ursaluna without doing the battle
Unfortunately not.
One particular Ursaluna has a unique form known as Bloodmoon Ursaluna. This Ursaluna is always male and its form cannot be changed. It is the only Ursaluna that is known to exist in the present day, and cannot evolve from Ursaring.
Ursaluna (Bulbapedia)
