Red/Blue - It's genetic code is irregular. It may mutate if it is exposed to radiation from element Stones.
Yellow - It's genetic code is unstable, so it could evolve in a variety of ways. There are only a few alive.
Gold - It has the ability to alter the composition of its body to suit its surrounding environment.
Silver - It's irregularly configured DNA is affected by its surroundings. It evolves if its environment changes.
Crystal - Its ability to evolve into many forms allows it to adapt smoothly and perfectly to any environment.
Stadium - Its genetic code is irregular. It evolves into three kinds of Pokemon when exposed to the radiation of elemental stones.