The Assassin is an incredibly useful class to have on the field, but also one to be fear should you face one. Like their Thief counterparts, they still retain their abilities to Steal and Lockpick, as well as their weapon proficiency in only swords. What the Assassin does gain however, is the ability to be a formidable combat class. On occasion, the Assassin will preform a special critical hit, in which they will defeat an enemy in a single attack, regardless of health and defense. These versatile characters are a valuable asset to any force.
It's important to keep in mind that Assassin and the Thief are different classes in combat. The fragile Thief loses much of it's weakness once promoted. Although their defense and health is moderate at best, it's rare for an assassin to fail to evade an attack (unless the difference in level/weapon triangle takes to great of an effect). Capping their stats out at a disappointingly low strength, it's not unheard of to strike for zero damage on the more heavily armored foes. Be aware of the accurate attacks of Mages, as they'll be able to take advantage of your high speed, yet moderate defense.
Being the promoted version of the Thief, the Assassin can not be promoted any further.