Monte Cristo Mythologie: The King of the Cavern (巌窟王, Gankutsuō?) is the way of life of Edmond Dantès, acting as the incarnation of revenge, sublimated into a Noble Phantasm through his manifestation as an Avenger. As he did not fit under any other sort of class, his body that manifested as Avenger was converted into a Noble Phantasm.
It allows him to attack by using magical energy like a poisonous flame. His body is immune to all sorts of poisons and mental inference effects. It also allows him to conceal his parameters and class, displaying false information to others. It is a continuously-active-type-Noble Phantasm, but it also has an effect when releasing its True Name that is not displayed in Fate/Grand Order which is to release pent up grudges in an area and provoke enemies to attack each other.