I need to know how to get a ninja greegree, as every time i try to kill one, i keep getting captured, anyone know?

Turn on protect from range and attack one of the monkeys down near that little jump bridge towards the east side of the island. That's about your safest place to attempt it.

 

 

 

If you don't already have a regular monkey greegree, you should get one by killing a Karamjan monkey and using that corpse to make one. Those monkeys will not attack someone using it, and you will need that particular greegree anyways to do the Recipe for Disaster sub-quest on Ape Atoll...