User blog comment:Xandermcc/Deathstroke is joining Team Arrow?/@comment-26624146-20170421093923/@comment-27700324-20170421135513

He'll kill someone in Oliver's life. Also i agree with your theory on Oliver teaming up with Slade now that it is basically confirmed. Since the trailer also confirmed that Black Siren is going to be the one to kidnap Quentin, (one of the things that motivates Oliver to reach out to Slade) I don't think she is turning to the good side because you just expose her to enough dobblegangers of family. Once she kidnaps her dad and by what we see Quentin is being beaten on by his bad daughter.

But when it comes to Slade. Yeah he'll kill someone. It is Slade. He has kept a lot of promises to Oliver and this one will also be kept.