The idea of mixing characters from different stories means that young writers can add new twists to the personality of these characters. Also they can write about how characters might react in unfamiliar situations e.g. How would Snow White keep the three bears on task! The idea of putting characters in different situations and describing how they would react comes from Mat Sullivan who talks about it in detail in his excellent book 'Developing Writing Through Comics'. However, mixing characters from different stories is an extension of this.
A next step from this would be to 'mash-up' characters from different narrative genres rather than just within the same genre. For example ' Harry Potter and The Minotaur'. This could lead to exciting new twists on well-known stories. Also, characters would definitely be placed in situations that are outside their comfort zones. Thus leading to deeper character development.
An idea from @gazneedle is to mash-up characters from famous films e.g. Harry Potter is tutored by Obi Wan Kenobi. This would open up opportunities for using digital media, many examples of which can be found on The Literacy Shed by Rob Smith.
@WatsEd suggested some fantastic ideas that character mash-ups could provide for comprehension and discussion prior to writing. For example :
Using a well-known story such as Little Red Riding Hood, ask 'What if...?' questions such as:
1. What if it was 3 bears, not a wolf?
2. What if Hermione was going to grandma's house?
3. What if Wolverine was at Grandma's house instead?
At a later date, we started to discuss images of mash-ups that could be used to inspire writing. A range of images such as the ones below was found by @grahamadnre, @redgierob, @gazneedle and @WatsEd.
This video is a mash-up of many superheroes.
How about Batman/C3PO
There are many more examples of images of character mash-ups on the internet. Visit Lee Parkinson's blog (link further up the post) to see an example of a brilliant app that could be used for character mash-ups.