So we all know about Missingno and M, and how they are related. The Pokedex database said Kangashakan can't evolve but can Mega Evolve. But I watched a video of someone catching an M, and when he fed it a Rare Candy it evolved to a Kangashkan. Lets strong a message I already said. The Pokedex database said Kangashakan can't evolve but can Mega Evolve. CAN'T EVOLVE! And a Pokemon that isn't fully evolved can't Mega Evolve until they evolve it to their non-mega form. It evolved anyways. How does this work? (sorry about my bad spelling)
As said by Shiny Hunter Luna above, there may have been a planned pre-evolution for Kangaskhan, but was later scrapped and some code for it was still left in the game. The coding for the pre-evolution of Kangaskhan is M, meaning that M can evolve into Kangaskhan. However, it has not been confirmed that there was going to be a pre-evolution of Kangaskhan to my knowledge. Because M is a glitch Pokemon and not an official pre-evolved form of Kangaskhan, it is not listed as an evolution of Kangaskhan on this site.