To spawn Mychal you must speak with the Earl Garrick, Ask him help, he will talk about mordred and errant knights, ask him errant, he will tell you that mordred is trying to recruit them and to bring him any information you find. Find an errant knight. Ask them mordred. They will attack you, they may spawn a map, get map corpse, give it to the earl, he will tell you to go kill Mychal. Mychal spawns at the Ambrosius dyke.