Mood Whiplash Smooth Transition

How do you do a mood whiplash well without it feeling out of place or just contrived?

Edit: To expand on this, how do you something that is seemingly happy to ther point of being a shonen but later turns into soemthing bleak and ugly? I wanted to know how you can create a smooth transition into darker and edgier without it feelign out of place.

edited 2nd Jun '11 9:02:15 AM by GAP

Have the "darker" events be a clear and logical effect from the previous ones, a natural consequence of them. Don't just throw around random coincidences that suddenly change everything without any kind of foreshadowing.

edited 2nd Jun '11 9:04:00 AM by Dealan

One thing that might work really well is to take something that could turn out very badly if it weren't for Plot Armor, and take away the Plot Armor.

So, for example, let's say the guy is getting badly beaten, and then he pulls out his Dangerous Forbidden Technique. Normally, Plot Armor would dictate that a) he's going to win, and b) the technique won't be nearly as dangerous as it was made out to be. Take away the Plot Armor, and he loses the fight and/or gets seriously injured by the technique he used.

That's called Reality Ensues, and it doesn't have to be Darker and Edgier (though it often is).