NFE SpDef Spinner (Tentacool) @ Eviolite 
Ability: Liquid Ooze 
EVs: 248 HP / 8 Def / 252 SpD 
Calm Nature 
- Rapid Spin 
- Knock Off 
- Scald 
- Rest / Toxic 
Optional Move(s): 
- Acid Spray
- Sludge Bomb
Optional Item(s): 
- N/A 
Optional Ability: 
- N/A 
Optional EV/IV(s): 
- N/A 
Overview: With access to Rapid Spin and Knock Off, Tentacool offers decent team support. Its main niche is its ability to check Roselia, the premier Spiker, somewhat reliably thanks to its solid defensive typing, Liquid Ooze, and high Special Defense stat, whilst also being able to spin away any Spikes it tries to set up. However, Tentacool faces competition from Mareanie as a Water/Poison-type, which is a better mixed wall, since it has access to more reliable recovery and a better ability. Tentacool also has to compete with Wartortle as a Spinner. Wartortle boasts much better overall bulk, as well as useful utility options in Seismic Toss, Haze, Counter, and Mirror Coat.
SpDef Spinner: Maximum investment in both HP and Special Defense lets Tentacool act as a reliable check to Roselia, Magmar, and special Monferno sets. Rapid Spin clears any hazard on your side. Knock Off removes Eviolite from opposing Pokemon. Scald is a moderately strong STAB move which can also cripple opposing targets with a burn. It also 2HKOs frail Fire-types such as offensive Monferno and Combusken. Rest gives Tentacool a form of recovery, although a Cleric is normally needed to support it. Alternatively, Toxic can be used to cripple bulkier switch-ins such as Servine, Marshtomp, and Quilladin. 
Checks and Counters: Ground-types such as Gabite, Marshtomp, Krokorok, and Vibrava can all force Tentacool out with a STAB Earthquake. However, none of the aforementioned Pokemon appreciate a potential Scald burn. Psychic-types like Kadabra, Metang, and Duosion can all OHKO or deal significant damage to Tentacool. Electric-types such as Electabuzz and Eelektrik can both switch into Tentacool relatively easily and either deal significant damage to it or force it out and gain momentum with Volt Switch. Tentacool's poor physical bulk means that it struggles to switch into almost any physical attack. Due to Tentacool's passive nature, setup sweepers with reliable recovery such as Clefairy, Duosion, and Klang are able to set up on it and aren't affected by the occasional Toxic.