start the mission and give him the final blow and you get it. Nemesis wont escape as long you are online and don't get reconnected, so wait until 0 and if you want update the remaining RP some times as long you have medals. The 777 HP is easy to, you remember(or know) the art Essence Exchange from Yelv? yeah right thats the key! just collect close to 777 SP, but more not lower. use is at now in a