Very Rare
Scroll of futuresight
technique
At the end of every safe rest roll a d20. Until the next safe rest you can expend it, to replace any d20's result with it.
Rarer/more advanced version: you can choose which die to roll and replace any die of the same size with it.
This technique can be learned by studying the scroll (upon which the scroll magically dissapears) or taught to you by a master of the technique.