Overall there are 8 greegrees, including the large and small ninja greegrees, large and small zombie greegrees, bearded, blue faced and normal gorilla greegrees and the Karamjan greegrees.
The greegree is mainly used in Recipe for Disaster but also can be used to avert being attacked on Ape Atoll.
The different greegrees can be combined by using one on another. This adds both of the greegrees to a list that can be accessed via the Swap option on any of the greegrees that the player owns, and in the process deletes the greegree that was used on the other. The greegree can then be turned into any of the greegrees by selecting it in the list. The greegree cannot be swapped into another while it is equipped, but it is possible to equip another to change forms.