Master Yaddle of the Jedi Order was one of the most respected and highly skilled Masters that the Order had ever seen… That was until her disappearance just before the Clone Wars.
But during this time she rediscovered an ancient and lost Light Side force ability known as Morchiro, causing great shock among the other council members. This force ability allowed it’s wilder to rapidly slow down the bodily functions and vitals of an opponent, all the way until the point of death.
After realizing what this ability could do, it was immediately Forbidden and all knowledge of it was hidden away deep in the “Classified” Section of the Jedi archives, where only the highest ranking masters could view it. They considered the technique to be deeply dangerous and if the user did not have their mind firmly planted in the light side, they could easily slip into darkness.
Despite all of this though, they soon came to trust Yaddle with this power, and deemed her alone worthy to use it. Because of this, she discovered that the ability could actually be used on yourself. This would let you slow all of your vitals in a harsh survivial sitation, ensuring that you wouldn’t need water, food or even air for over a year at a time… So that was the FORBIDDEN FORCE ABILITY THAT YADDLE used and why the Jedi refused it!