4. Lugia (First Appearance: Pokemon Gold/Silver)
Lugia is an awesome, elegant, sleek looking silver dragon… bird. He is also the Guardian of the Sea, and in command of the single most powerful flying type move in the games (Aeroblast). He has insanely high stats (well, two of them, anyway), and some neat moves. Along with his typing (Psychic/Flying), and the fact that he can bafflingly learn water type moves, giving it a natural advantage over its counterpart Ho-oh, and along with the part that actually getting to Lugia, then engaging it in battle, then whittling down its HP to a level where it could be caught, and then actually catching the Pokemon, was so incredibly hard, Lugia became a bit of a ticket for bragging rights.
Even today, his popularity stands at an all time high- he single handedly propelled the sales of Pokemon SoulSilver version well past the sales of Pokemon HGeartGold Version, just as he had helped Silver sell more than Gold eleven years ago. Considering that Gold/Silver, along with their remakes, represent the only time that the ‘second’ version has sold more than the ‘first’ version, I think it is telling of Lugia’s popularity.
3. Mewtwo (First Appearance: Pokemon Red/Blue)
I’ve never been a fan of Mewtwo much personally (he was a bit gimped in the original Pokemon games, because of his awful moveset), but one cannot deny the sheer pervasiveness of this Pokemon. Mewtwo became a pop culture phenomenon, he became symbolic of every trainer’s quest to have the ultimate Pokemon, and, as the single most powerful Pokemon of his time, he spawned a lot of urban myths and legends, quite a few of which still persist to this very day.
Mewtwo has incredible stats- until Arceus came along in Pokemon Diamond/Pearl, he was the most powerful Pokemon across all games, period.
However, it isn’t his appearances in the games that have caused him to be so popular, it’s his appearance in the movie (Pokemon: The First Movie to be specific, though he did show up in Mewtwo Returns too) as well as tantalizing glimpses at him in the cartoon that made him so cool. Mewtwo in the movie was a veritable badass, and he was insanely powerful, so it can be understood why he appealed to the Pokemon demographic so much. His popularity was so enduring that even today, when there are polls on the best Pokemon ever, Mewtwo frequently tops them.
2. Gyarados (First Appearance: Pokemon Red/Blue)
When James kicked his Magikarp off the raft and into the sea, only to cause it to evolve, we knew that he was in deep shit. You see, Gyarados looks frightening. He looks mean, he looks nasty, and like no other Pokemon, he looks like he means business.
He also has some incredibly typing, leaving him weak to only one type effectively, unbelievably high stats, great attacks, he looks awesome, and he is relatively easy to obtain and train. The problem usually is getting Magikarp, his unevolved form, and also the single most worthless Pokemon in the games, to actually win enough fights to evolve into Gyarados. Trainers who persist are rewarded with one of the best Pokemon possible for their teams.
Seriously, every self respecting Pokemon trainer has a Gyarados on their team. It’s like a law.
