There are 13 death animations in the "Test Your Might" tower. When you fail a challenge, you will get killed. The death sequence is completely random. You can get all of them in the very first challenge. Simply press R2 when the challenge begins to fail immediately. Retry the challenge over and over again until you get all 13 death animations to get the "Not Dead Yet" trophy. It takes approximately 20 minutes to see every death animation once (depending on how lucky you get).