Final vows adds a potion of final vows, when drunk it is a permenant effect, that once upon death will activate. it will ressurect you, and let you say a final message, you get at maximum 1 minute but you can end it early when pressing "G" After someone dies under the effect of final vows a gravestone will appear. 0 experience yields a mossy grave 10 experience yields a cobble grave 20 experience yields a stone grave 30 experience yields a gold grave 40 experience yields a diamond grave
You can also craft a will with paper and a feather and enchanting bottle. When you right click the will you can assign a name and an item, and then upon creating a grave only the person in the will can access the item at the grave.
If you want to remove a grave, you can craft a gravedigger's shovel. when sneak right clicking it will destroy a grave, but with bad effects.