Octillery

Boasting the highest Special Attack stat in the tier, a fantastic typing of pure Water, STAB Surf that hits several common Pokemon such as Dugtrio, Ninetales, Graveler, and Rapidash for super effective damage while 3HKOing most neutral targets; RestTalk for longevity; and the complementary coverage of Hidden Power Electric or Ice Beam, Octillery makes for a phenomenal choice on many teams. However, while Octillery is amazing, it is not flawless. Octillery is quite slow, being outsped by most offensive threats such as Weezing, Stantler, and Xatu. Additionally, while Octillery is generally bulky enough to handle Pokemon it needs to with RestTalk such as Rapidash and Dugtrio, it can be 3HKOed by strong unresisted STAB moves such as Stantler’s Frustration and Fearow's Double-Edge or a sufficiently strong coverage move, and it can very easily be pushed into 3HKO range of attacks such as Xatu's Psychic by the ubiquitous Spikes. Octillery also has issues with coverage, as with Ice Beam, it is walled by opposing Octillery and Dewgong, while with Hidden Power Electric, it cannot touch Grass-types like Gloom and Exeggcute. Octillery also suffers minor competition with Dewgong, which in exchange for a much weaker Surf, the inability to effectively utilize Hidden Power Electric, and weaknesses to Rock and Fighting along with a lack of a resistance to Fire, provides much more speed and bulk than Octillery and a stronger Ice Beam, resulting in a a significantly superior matchup into Xatu and Fearow. Dewgong also has access to Encore, providing an additional niche that Octillery doesn’t have. However, Octillery's greater power, which lets it 3HKO Stantler and sometimes Wigglytuff, and its better/more practical defensive utility and pure Water typing making it a much better check to Magmar, Sudowoodo, and Sunny Day Ninetales often make it the superior choice on teams.