A person who looks uncannily like a mixture of two other people, so much so that they appear to be the offspring of the two other people (usually of the same gender).
"Hey, did you see that new croppleganger?"
"Yeah, she totallylooks just like Kate and Jill!"
Where a doppelganger is someone's exact double, a croppelganger is two people's exact double, but fused into one person. This person also must not be related to the other two.