Due to their healing it's very hard to kill them solo. A medium level knight should have no problem blocking it as it's attacks aren't extremely powerful, however you will need 3-4 shooters (preferably Paladins, as Mages cannot deal much damage to these creatures), otherwise you will be wasting a lot of supplies. Be wary when group hunting, they will retarget relentlessly. Also, higher level paladins could kill them solo using Assassin Stars and Divine Missile. Try to stay always diagonal when killing it solo as a paladin, since the poison wave decreases 95% of your distance fighting for about 3-5 seconds.