Below is the medallion rating, from best to worst:
With a health level below 20%, it increases the chances of dodging. If you combine it with other evasive items/ skills, you will increase the survivability of your hero, which will help in passing difficult chapters.
At a health level below 20%, it increases protection against projectiles. It’s not a big deal, but it blends in well with Ghost Coat so you can survive another enemy strike.
It works as a last chance to save you from a killer shell. So, instead of dying, you keep your health and get invincible for a short time. Note that the medallion works once.
The Iron Locket
At a health level below 20%, it increases protection during a collision with enemies. But with this low gain, you’ll survive another hand-to-hand impact at best. Not a very useful thing.