Get 4 stone gates and you don't have to necessarily trap it, just stop it from going at you, let it occasionally hit you and get it below 2k health with a Rock Drake AND USE A LIGHT PET and maginfying glass to check health. Once below 2k let it have a few swings, dismount, turn light pet off and hold up a metal shield and keep the Rock Drake close by, should impregnate, then get the f out outta there. It's alot easier then it looks.

More Reaper Taming & KO Tips