Curse of the Cave Dweller

Emanating in a sphere 250 feet in every direction is dim darkness that can only be seen through spells of above 6'th level and can only be destroyed by spells of above 6'th level. Dark sight Truesight and blindsight can see through this. If someone dies in this area they make a WIS Saving throw DC 15. On a Sucess, they can use 3DX Hit Die equal to their own On a fail, they die then they turn into a gargoyle. They cannot move and are completely normal for 5 turns, and then they can move as normal attacking close-by adventures, but unable to leave the area unless they move into another plane. During this time if they die they turn back to normal, for the next 2 years. After that, they are normal Gargoyles, but then for every two more years they spend there they change and all other monsters change evolving into different special creatures, randomly.