Ah, the Sugar Apocalypse... is there anything more twistedly fun than taking a peaceful, harmonious universe and dropping a hellgate into it and watching as The Smurfs becomes a scene out of Warhammer?
Part of the fun comes from how this can frequently emerge from the standard mechanics of many a Sugar Bowl; many of these universes carry the seeds of their own destruction.
Y'see, despite being a Lighter and Softer version of Real Life, most of these fluffy worlds still have some semblance of real life in them, including human vulnerabilities and flaws, and in order to preserve the harmony, many of these Sugar Bowl environments are only able to defend themselves from trouble because lets face it; the opposition is as cute and cuddly as the heroes are. You sometimes get the impression the only reason nobody has taken over and installed a horrible dictatorship is the fact that Mr Meanies attempts to waylay the local inhabitants may be more than a little half-hearted. This makes Pulling the Thread on some of these worlds somewhat easier to do than it would be to plunge a real world location into horrible chaos; at least in real life we know the world is a horrible place, we recognise this, and we have long, convoluted and frankly ingenious defences around our society to stave off potential catastrophies.
Drop these forces into the blissful environs of certain Sugar Bowl worlds, and you get an effect similar to what would have happened in if aliens had landed in Medieval Europe and gone to town. The results can be either tragic, or darkly hilarious.
Shock factor is a big part of what makes this trope effective. If the audience is expecting the colourful world to descend into Mordor, then the story becomes a depressing exercise in Tragedy. This may still make for an effective story as the hero has to find a way to restore the once vibrant world, which may at the end have permanently lost its innocence, but for the full effect to hit the audience, either with the purpose of getting them to buckle at the audacity or stand still in shock and revulsion, they have to not be fully expecting it to happen. This is, for example, the impact the Belgian advert run by UNICEF sets out to have on the audience; it starts off with a familiar scene, the Smurfs intro, familiar to adults across the world, and then... the bombs start dropping. The advert lets the shock set in, and only then delivers its message; that war destroys innocent children's lives. It was only done with that particular world, rather than in a series of adverts, because the trope simply wouldn't be as effective a second time.
