There are two different ninja greegrees. This type is made using bones from the Monkey Archers or the Monkey Guards summoned by Ape Atoll residents (level 149), although players don't have to kill the summoned guards (Karam kills them). There is a glitch if you get caught and you try to switch back to your monkey form, there is a small chance you will lose your greegree. However this glitch is not common, also if you have a full back pack, and teleport from Ape Atoll without removing your greegree, you will lose it. The sleeping monkey does not summon guards.