Tentacruel

Water

Tentacruel's good defensive Water / Poison typing most notably allows it to resist Fairy and Fighting, both of which can have an easy time against Water, as well as Poison and Bug. Its high base 120 Special Defense, ability Liquid Ooze, and Grass neutrality allow it to switch into one of Water's biggest threats; Mega Venusaur. It also works well as a Clefable check, wearing it down with a combination of Acid Spray and Scald. In general, its great Special Defense stat allows it to switch into special attackers with relative ease. Furthermore, its base 100 Speed is above average for a rather defensive Pokemon. Despite Starmie being the more offensively suited option for a spinner, Tentacruel offers immense support as the superior defensive spinner and should definitely be considered should you be looking for one. Moreover, it functions as a good stallbreaker with Acid Spray, can set Toxic Spikes for its team, can reliably use Rapid Spin to remove entry hazards, and forces switches on setup sweepers such as CroCune and Calm Mind Clefable, therefore providing a large and unique set of roles among Water-types.

Unfortunately, Tentacruel is outsped by most Ground- and Psychic-types and hit super effectively by their STAB moves. Steel- and Flying-types are immune to Toxic Spikes, with the former walling Tentacruel and the most of the latter being able to hit it for good neutral damage. As a result of running no Special Attack investment, Tentacruel heavily relies on the foe's Special Defense drops from Acid Spray or other means to actually deal a decent amount of damage with its STAB moves. In addition, its below-average physical bulk prevents it from being able to face physical attackers without taking a lot of damage, and in most cases, it is simply setup fodder due to its inability to deal much damage back. It also lacks reliable recovery, meaning it is worn down very quickly and finds itself pressured to remove or set entry hazards, so team support is crucial.