This is an attribute possessed by some Servants which warps, deforms and changes their appearance and powers based on the events in their life.
This skill comes from the slander and wild rumors that these famous people once bore. It is like a curse.
This skill tends to belong to Servants who committed atrocious acts when they were alive, but some Servants who have this skill were simply disliked because of the great power and authority they held in their time.
In Fate/EXTRA Vlad III and Elizabeth have this skill, and we can see some significant “Monsterization” in their appearance and actions.
The popular Monarch famously said, “Doing a poor job of carving your name in history can be quite scary nyaa.”