Basic Trope: A character who mainly exists to argue and point out flaws in ideas.
Straight: Bob is a member of the Awesome Hero Team, but his role is mainly to argue with the hero, Jack, as well as to point out what he thinks are flaws in his logic.
Bob is pretty much incapable of agreeing with anyone.
Whenever Jack changes his opinion, Bob changes his to remain the opposite of Jack.
Downplayed: Bob argues more often than not, but also agrees a fair amount of the time.
Justified: Bob is playing devil's advocate - he doesn't disagree with the plan, he just wants to make sure Jack thinks everything through before he leads the team into danger.
Inverted: Bob immediately and completely agrees with anything Jack suggests.
Subverted: Jack suggests a plan, and everyone looks at Bob. He says "Good plan."
Double Subverted: "...if you were to do this and this, that is..."
Parodied: Bob can't agree with anyone on anything, no matter the topic. If Jack wants to order pizza for dinner, Bob will suggest Chinese. If Jack suggests swimming for their recreational activity, Bob will suggest hiking, and so forth.
Zig Zagged: ???
Averted: Bob only dissents when he has a personal reason to object to the plan, but no more than that.
Lampshaded: "Anyone have any objections to the plan? Of course...what's the problem, Bob?"
Invoked: Bob is hit with a gypsy curse that makes him disagreeable, so this is the end result.
Exploited: Emperor Evulz sees Bob and Jack arguing and tries to convert Jack ("...you can't even control your own team..."), Bob ("...he's not listening to you..."), or both.
Defied: "Anyway, that's the plan. And I don't wanna hear anything to the contrary, Bob."