An upgrade to the Melchior and the Miraclious, and a rather large step-back in comparison to the Casper and the Droomzen, the Valhallan is pretty much a Droomzen with lowered stats due to having an almost-identical skillset. The only difference is the Absolute Zero it has in replacement for the Flame Thrower skill, which in addition to causing Ice-elemental damage to all the vanguards also reduces their speed. Try to defeat it quick to avoid getting your speed lowered too much, and to also cause some damage to the other enemies by triggering their Induced Explosion passive skill.