Thief type champion

So I was just thinking about what a cool champion in my opinion would be and came up with a concept. I came up with a champion who is a thief but not a normal thief he can steal things that don’t have physical forms. He can do this by using a sort of stealing magic. I was thinking his abilities would be something like stealing enemy hp or mana, taking hp from enemies and using it to empower a knife of his or a sword, for his ultimate it could be something like he can steal an enemies soul for a couple seconds, while he has their soul he cant hurt them and they cant be hurt but they cant do anything. Let me know what you think.

The link is to a picture that shows what the champion would maybe look like. I would just post on here but its not letting me.