The Green Knight is not deployed with the rest of the army, but follows the entry rules for Ambushers instead, with the following exception that he may appear in the first turn instead of the second.
When the Green Knight is awoken, he must be placed in either a forest or a water terrain piece anywhere on the table, but otherwise follows the rules for Ambushers as normal. If no forest of water feature is present, he may enter from any table edge using the normal rules.
During the game, the Green Knight may disappear at will and reappear in another location completely. If the Green Knight is within (or moves into) a forest or water terrain piece during the Remaining Moves phase, then he may instantly be removed from the table and replaced anywhere on the table within another forest or water terrain piece, facing in any direction. He may not move any further that turn. Note that he still may not end his move within impassable terrain.