You should know about Aika
Here are some tips I have collected about stealth, which should provide a good starting point for owning more aika online gold in Aika.
Load up on Seeds of Destruction. This will allow you to see low level assassins, and all rangers who have Hide 1 only. To see advanced stealth you will need the All Seeing Eye ability. Seeds of Destructions are extracted, but cheap enough at the Broker as well.
As an assassin, there are no special attack abilities to use from stealth. Instead you need to make sure that you learn your positional abilities well, so that you can sneak up on your opponent from the right angle.
Learn the limitations of the stealth abilities, Hide 1 and Hide 2. None of these can be used in combat, and Hide 1 can be seen by any class if they have Seeds of Destruction.
If you want infinite stealth, you need to save up and get hold of the Shadow Walk I stigma skill, which is a rare drop. But it has a 3 minute cool-down, and lasts for 5 minute, so it is infinite stealth effectively. It uses advanced stealth mode as well.
If you want an ability to allow you to stealth in combat, there is not really a useful one for PVP. Wind Walk I do allow you go into advanced stealth for 10-20 seconds, but require 3000 divine points, which is more or less impossible in most PVP scenarios. Hopefully this guide shows you some of the tactics and skills you should be using.