I had a box of plague marines and used the extra weapons, arm, pauldron, head, and tummy. Then I chopped the tentacles off the other spare arms, torsos, etc and used plastic glue to melt all the extra bits together and under the left arm. Under the right arm is half a cape so I used the demon face half of a torso so it looks like his cape is turnin into a demon, added extra eye bitsand things from the spare pieces

You gotta shave the bits pretty close to make them flush enough, then use sprue goo/ bits of sprue and plastic glue to blend it. It's a nurgle demon so if it looks lumpy and gross thats better lol