Assassin

Merciless and lethal, the Assassin stands for treachery and surprise attacks. Although there are a lot of thugs, bandits and murderers that roam the realm, the assassin is one of the few who have made a real profession out of killing. Usually organized in small groups, Assassins are trained in the arts of fighting dirty with backstabbing and stalking. Although they are formidable fighters, those hirable murderers prefer sneak attacks on unsuspecting victims which, they will attack with all kinds of dirty tricks to gain the advantage. Depending on their current mission, the Assassins work alone or in small hit squads. They are rarely encountered in greater numbers except by those that are unfortunate enough to stumble on their hideouts.
They give some rare loot which makes it worth the supplies used.

Assassins won't run away when in low health.

An assassin attacks in melee range.

Mages and Paladins, should wear a Dwarven Ring to run these without problems and Magic Shield will also be useful for Mages below Level 20. Some area runes, like Fireballs and Heavy Magic Missiles might be useful, for when they turn Invisible. Their invisibility only lasts a few seconds though, so you should not have a big problem fighting them without the area runes.