In the Crash Bandicoot series, Fake Crash is an odd character who tends to randomly appear with no reason or context. He has a goofy and odd personality, and doesn't seem to take things seriously.
In Skylanders, Fake Crash shows a more sinister side, hijacking Cortex's Matrix Chamber and terrorizing the Wumpa Island by disrupting the island's rhythms for apparently no reason.
Story
Fake Crash's origins are unknown. He was presumably created by Dr. Neo Cortex or Doctor Nitrus Brio, like all other mutant characters in Crash Bandicoot. He is a neutral character and usually only appears via random cameos and background appearances.
Skylanders: Imaginators
As Cortex was preparing to use his Cortex Matrix Chamber to create an unstoppable army of minions, Fake Crash hijacked the machine without his notice and used it to send bad rhythms across Wumpa Island, threatening to tear the islands apart. Eventually he was defeated by the Skylanders.
He was created when developers at Naughty Dog (the original game developers of the Crash Bandicoot franchise) had seen a bootleg plushie of Crash from Japan, which included both the large teeth and eyebrows. Oddly, Fake Crash became a second mascot of sorts of the franchise in the country, as well as appearing on the second remake, Crash Team Racing Nitro-Fueled.
He is the first guest character to be a boss.
His only differences between him and the real Crash are different eyebrows, darker color, smaller pupils and bigger teeth.