Here Odin is trapped in Midgard, only having parts and fragments. He lacks most of his power, and needs to open the bifrost in order to obtain them. He lost his memory at Ragnarok, but became mortal, and was sent to Asgard. There he learned as much as possible, speaking with and listening to anyone who had a story to tell. He then slowly pieced his own story together, and was able to conjure what magic he had left to return him to Midgard, the only place he could go, and give himself a weak power of prophecy. The idea is to tell the tales of Odin to make him out to be the bad guy, and the Giants out to be the heroes of the stories, but when it is revealed to the players that this Seer is indeed Odin, he will tell them of how from before Thor was even born, before Odin could even be a father to him, the Vanir and the Jotun foresaw that he would be a rage filled, murderous brute, who would slay so many that he would be the reason for the end of the world. Essentially, Odin’s motivation is one of revenge, for his son being doomed from before he was born, and to avenge the death of his son with the lives of every last Giant.