What are monochrome Pokemon?

Question

My Internet is a little slow (don't know why) and some pages don't even open.. I can't play Showdown but I will resolve this problem later, this page that everyone is talking, I can't open it :c

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I don't have XY and while I was searching on the PokemonDB I found something called ''Monochrome Pokemon''.
Pokemon's normal sprites are turned into black and white if I'm not wrong.

Now what I want to know is

• What are the Monochrome Pokémon
• Why do they appeared in XY?
• Are they more rare than shinies?
• What are the chances of finding them?
• Does it cause you problems to your game file?

Answer 1

Monochrome Pokemon began as a rumour. Here is the Marriland forum discussing them, and they're referred to as a 'texture error', which is either a small glitch or deliberately made by hackers.

This Game FAQs thread also discusses it, and monochrome Pokemon seem to appear in the wild/ on the Pokedex/ on screen, but then switch back to their original colour.

So to sum up, they are not another version of shinies, i.e. a super rare Pokemon, and they are not obtainable (or at least won't remain monochrome). If it happens naturally in your game, it should just be a colouring error and do no harm to the game itself.