Minecraft 2.0 is an April Fools update that showed pig horses, zelda chickens, and coal blocks.

But it also added things that will never be added in the game, like flying sheep, fish droppers, and redstone silver fish.

These Blue Ore Chickens made their way into the game when being at diamond and lapis spawning height. When chickens do that they turn to DIAMOND CHICKENS! (This is not implemented in the redstone contraption)