The Party's First Encounter with Asgan

This will begin when the party is around 10th level, having established some notoriety for themselves. They will have seen some random bad guys, but will discover the true puppet master of the plot is the dark figure from one of the PC's past, Asgan the Chosen . They will find a haiku Dusk // Dawn in pieces, which will allow them to piece this together over a long period of time.
Upon figuring this information out, they will eventually stumble into a meeting time, or similar indicator of his presence. They will likely sneak in to this meeting, in an attempt to thwart it or gain intel, but he is always prepared and brings heavy guard who are well-trained at protecting against this. The party will have to figure out a way into the building and then navigate this castle-dungeon, dodging security like Sly Cooper and eventually find themselves in a position to overhear and see this conversation. Their target is a cunning, ruthless person who speaks only as much as needed but says volumes with few words. This will be a sharp game of verbal tennis with Asgan the Chosen seeming to always be one step ahead of his counterpart. Around this time, some noise will draw attention to where the party is hiding and its up to them to decide whether to stay (and definitely lose) or to make a daring escape! He will not hold back on intruders, and sends several waves of guards to find them. Once they seem to escape, a flying guard will land near them escorting their leader. Epic flying mount fight (griffons, wyverns, small dragons?), with him leaving the party to his capable guard and stays flying to watch. If it looks like his guard is losing, he will drop in, do a LOT of damage to the party, and grab his guardsman and fly away.