6. Kingdra
Kingdra was the only Dragon type Pokemon introduced in Generation Two. It's not just a Dragon, though, and as the evolution of Seadra it also carries the Water type. In the Gold & Silver games the final gym leader for the Johto region has a Kingdra in her team and it was always a nightmare to take down. Personally I can think of very few gym battles over the five generations of games that have caused me such frustration and so it is a surprise to see so few competitive teams include it. Water and Dragon types are two of the most popular types employed in competitive battling teams and Kingdra is proficient in both, making it an excellent way to utilise these key types but only take up one space on your team. Kingdra's dual type also limits the amounts of weaknesses it has. Its Water type makes it the only non-legendary Dragon resistant to Ice attacks, and its Dragon type removes the Electric and Grass weaknesses its pre-evolution has. Only Dragon attacks offer super effectiveness against it. Kingdra is one of the most balanced Pokemon in terms of stats; its Attack, Defence, Special Attack and Special Defence stats all start of identical. Its an all round powerhouse that can dish out serious damage as well as take it. It can have the ability 'Sniper' which increases the power of critical hits. Coupling this with an item that increases the likelihood of critical hits occurring can be a huge pay-off. Many of the most popular Pokemon in competitive battling are included for convoluted or strategic gain. Kingdra is not one of these. If you've filled five spaces with tricksters and tanks then you'll definitely want to consider Kingdra as the powerhouse that can seal the victory in the end when you need to put the big hits in.