I got the Valhalla's warriors once. I dont know if it was a mistake or what but have not been able to fight them since. They now pop up after I am out of stamina.
they would only pop up if your fight list is small or completely empty level 500 i think they open up try refreshing multi times that might force em on there
I have done that several times and the only time they pop up is after I run out of stam. I have wiped out my battle list and am left only with low health low guild people who give crappy exp. I start picking them off and run out of stam and then the valhallas pop up.
