Tentacruel

As a Water-type, Tentacruel distinguishes itself from its competition thanks to its secondary Poison typing and access to Swords Dance and Rapid Spin. With the former move, Tentacruel can act as a dangerous sweeper due to its good Speed and ability to exploit a lot of passive Pokemon like Forretress, Umbreon, and Blissey as well as other Water-types like Vaporeon and especially the omnipresent Cloyster. As a spinner, Tentacruel has a great matchup against the two best Spikes users in the metagame in Cloyster and Forretress thanks to its Toxic immunity and resistances.

However, Tentacruel's mediocre offensive stats mean that even with a Swords Dance boost, it fails to 2HKO important Pokemon like Snorlax and Zapdos. Additionally, crippling weaknesses to Electric, Psychic, and Ground mean that you cannot rely on Tentacruel to check the likes of Steelix, Marowak, Nidoking, and Rhydon, something you would typically want from your Water-type. These factors also mean that Tentacruel is plagued with a large number of checks like Raikou, Gengar, Misdreavus, and Starmie. Starmie is also a huge competitor to Tentacruel as a spinner due to its Speed and secondary Psychic typing, which allows it to better deal with common spinblocker Gengar and check Machamp much more effectively. Furthermore, Tentacruel cannot use Swords Dance and Rapid Spin on one set, forcing the player to choose what they feel will be most beneficial.