Have you and a guest signed in. go into a survival match at the dead center level. pick up a adreniline shot. have the guest go up 2 floors and stand on the railing. pull your adreniline shot out and stand in front of the guest and hold down X. On the guest controller you just hold foward and you will revive the guest like 4-5 times in one shot. i found this to be the easiest and the fastest way to do this acheivement.