Aion Assassins like the Rangers are based on the Scout class. The Scout has a skill known as Hide I and is obtained at level 5, which grants them the ability to be invisible to other players. Note that the invisibility is not permanent and only lasts for 2-50 seconds and is on a 1 minute cooldown. This is skill is also called basic stealth, when discussing types of stealth.

For Scouts who eventually become Assassins there is Hide II at level 34. This stealth can last up to 1 minute and is also on a 1 min cool down. However the movement speed decreases to 40% as opposed to 30% of Hide I. This level of stealth is know as advanced stealth.

Neither Hide I or Hide II can be used in battle. So if you get jumped on by another player in surprise, they will not help. There is, however, the Wind Walk skill that you obtain at level 31, but this has limited use in PvP since you need to 3000 DP to cast it. Getting 3000 divine points is not easy, though there are potions that can give you 2000 dp instantly that will help.

However, it is the Shadow Walk Stigma skill that high level assassins use when they reach 45. It allows you to go into advanced stealth for 5 mins, and has a 3 minute coolddown. Since the cooldown timer starts as soon as you enter stealth, you basically have infinite stealth with this skills. However, due to its nature, it carries a hefty premium when sold on the Trade Broker.

As mentioned there are two levels of stealth, basic and advanced stealth. Using items such as Seeds of Detection, every class will be able to see you in stealth. However, once you get advanced stealth there are two classes that you need to worry about, Rangers and other Assassins. At level 40, Rangers and Assassins get access to the All Seeing Eye. This skills allows the user to see advanced stealth for 30s, but is on a 10 minute timer.

You can attack from stealth, but there are no special skills that give you a bonus if attacking from stealth. Instead you should you look at the special attacks that give you a bonus by attacking from a particular position, such as Surprise Attack. This skill, gained at level 25, gives a big bonus when the target is attacked from behind.

Aion stealth it not as powerful as stealth found in other mmorpgs, and the Aion Assassin stealth is a more tactical style of gameplay. But by understanding the limitations of Aion stealth, your Assassin can still be an effective PvP player, especially running around solo in the Rift.