What is AG?
AG stands for the Advanced Game. The first lands implemented were Annwn and Rift Glacier (around the time when the Basic Game only consisted of Kesmai and Axe Glacier). Torii was then added, followed by the land of Shukumei at a later point in time.
The Advanced Game offered tougher monsters to fight, better weapons and items to acquire, and most of all new content to explore. There were only 2 portals to the Advanced Game, one in Axe Glacier (where the Underkingdom portal resides in LoK) and one on -4 Kesmai (which became a portal to Oakvael in LoK). Going to Advanced Game was a PERMANENT trip, and you could never return to the Basic Game with that character.
(The Advanced Game was never implemented into the Legends of Kesmai game, and remained an Island of Kesmai exclusive.)