First off. The majority of the parts you'll need are found in these sets
Lord of Skull Spiders
Mask Maker vs Skull Grinder
Umarak the Hunter
Umarak the Destroyer
Please note that you'll need an extra ball joint, there isn't enough in these sets. http://www.bricklink.../PL/53585.jpg?0
Next, I used this video, which is very useful if you want a step by step guide, and which parts to gather.
Don't worry about the coloring, just use the parts from the sets, and you'll be fine.
HOWEVER. Please stop the video at 5:42. Do not build the following part, but instead use this image that uses Umarak the Destroyer's jaw piece. https://www.flickr.c...57670900951320/
And that's about it. Everything else should be simple and easy. If you need any help, feel free to post a comment. I'll be happy to assist.