Rapid Spin users have not been easy to come by in NU ever since Cryogonal rose into RU. However, though one of the few remaining spinners, Wartortle still struggles to carve itself a niche against its competition, Armaldo and Torkoal. On the one hand, Wartortle has the unique ability to virtually guarantee a Rapid Spin with the use of Foresight, bypassing spinblockers entirely. It also boasts a great defensive typing alongside effective base 145 defenses with Eviolite and maximum EV investment. Furthermore, Wartortle has access to several useful support moves besides Rapid Spin, such as Haze and Yawn.
On the other hand, the Turtle Pokemon suffers from several severe limitations that make it less viable overall than its competition. Wartortle's offenses are very low, forcing it to rely on either a weak Scald or Seismic Toss to damage its opposition. It also has no recovery besides Rest, which means that its excellent bulk will only take it so far defensively. Overall, Wartortle doesn't do much besides spin and take a few hits, which renders it quite single-purpose. However, the ability to nearly guarantee a spin with smart use of Foresight and Rapid Spin is a small but effective niche that Wartortle can call its own. If for some reason Torkoal and Armaldo just won't fit on your team, Wartortle remains a viable spinner.
Rapid Spin is literally the only reason to use Wartortle, so it's no surprise that it's the main focus of its most viable set. While Wartortle would ordinarily have a tough time getting past opposing spinblockers with its weak offenses, it can use Foresight to completely ignore Ghost-type Pokemon's immunity to Normal-type attacks. Scald is Wartortle's main option for dealing damage, and while weak, it does decently hurt Pokemon that have low defenses or are weak to it; it also has the bonus of being able to burn and possibly cripple the opponent. Due to Wartortle's pitiful Special Attack stat, however, you might be inclined to run Seismic Toss instead. This will provide Wartortle with a more consistent method of damage, and it will also prevent Pokemon such as Gardevoir from setting up Substitutes that Scald would be unable to break. The last moveslot should usually be dedicated to Haze, as you are otherwise vulnerable to opposing setup sweepers when Wartortle is in play.Team Options & Additional Comments >>>
Despite being limited to a very specific niche, Wartortle does have a few other options that could have some use. Due to Wartortle's great bulk, it is capable of taking a hit and dealing a substantial amount of damage to the opponent with Mirror Coat or Counter. Unfortunately, this would require excellent prediction to pull off, and it could be a waste of Wartortle's valuable health. Ice Beam can do plenty of damage to some Water-type resistant Pokemon such as Altaria and Cacturne, but it's fairly weak otherwise. However, it might have some use on an offensive spinner set alongside Surf. A Modest nature and an EV spread of 196 HP / 252 SpA / 60 Spe would be recommended on such a set in order to outspeed Pokemon with uninvested base 65 Speed stats (such as Flareon and Alomomola), and this would also allow Wartortle to heavily damage Golurk and almost always break the Substitute of an opposing Bulk Up Braviary with Surf.
Wartortle could support its team with Rain Dance while also taking advantage of Rain Dish, but as mentioned before, Rain Dish is illegal with many of Wartortle's key attacks. Even if that were not the case, Wartortle's need for Eviolite prevents it from holding a Damp Rock, which means the rain would only last for a couple of turns after being set up. Aqua Jet and Fake Out are two good priority moves, but they are useless on Wartortle. Its pitiful base 63 Attack stat leaves these moves fairly useless beyond killing off a Sturdy or Focus Sash user on its last legs. Refresh can be used to cure Wartortle of hated status afflictions, but it's generally more effective to just run Wartortle alongside a cleric.
Checks and Counters
Due to Wartortle being a support Pokemon, having a check or counter to it is hardly necessary. Because Wartortle has one main purpose—to spin—the main way to handle it is to prevent it from doing so. While Wartortle's main niche is the ability to bypass spinblockers with Foresight, any variant not running Foresight can be stopped almost entirely by Ghost-types (although Golurk will not enjoy taking a STAB Scald). Frillish and Misdreavus in particular have little to fear from Wartortle due to Frillish's immunity to Scald via Water Absorb and access to Taunt, as well as Misdreavus's ability to cure any Scald burns or Toxic poison with Heal Bell. Although a niche Pokemon itself, Shedinja can also spinblock even Foresight variants due to Wonder Guard.
Once you've moved past Rapid Spin, Wartortle isn't too hard to handle at all. Pokemon with powerful super effective STAB attacks are some of the few Pokemon capable of netting a OHKO on Wartortle, and these are usually capable of defeating Wartortle outright or forcing it to switch out. Roselia in particular is dangerous because it can force Wartortle out with its Grass-type STAB and set up its own hazards, while also being immune to Toxic and able to heal Scald burns with Natural Cure. Pokemon with 101+ HP Substitutes are dangerous as their Substitutes will usually take two Scalds or Seismic Tosses to break. Bulk Up Braviary in particular can easily boost against a Wartortle that lacks Haze, while still setting up Substitutes with ease against those Wartortle that do run it. Overall, anything that isn't weak to Water-type attacks and won't mind a Scald burn or the occasional Toxic can handle Wartortle just fine.