Anyone who has played the original Dark Souls will find Scorpioness Najka looks a wee bit familiar--she's basically a scorpion version of Chaos Witch Quelaag. In practice, her attacks are fairly easy to dodge. If you keep your distance, she'll cast soul arrow-esque magic spells your way, some of which can track your location.
Up close, she has short range with her front attacks, but watch out for her tail--whenever she slams it into the ground in an attempt to kill you, take that opportunity to dish out some damage. Our video above explains the fight in more detail.
For more help be sure to check out our complete Dark Souls 2 Boss guide.