Pokemon's First Appearance: Pokemon Gold, Silver & Crystal

Sure, Celebi isn't the most powerful Pokemon on this list (it's practically weak to almost every Pokemon type), but this half Grass, half Psychic creature is nearly unmatched in speed, skill and stamina. It has a decent selection of non-damaging and damaging moves (such as Solar Beam and Psychic), and has one of the best base stat totals of any Pokemon. (600 to be exact.) Plus, it's adorable.