Moves
Shell Smash boosts Tirtouga's offensive stats to incredible levels, allowing it to easily clean late-game. Waterfall is Tirtouga's most reliable STAB move and has a chance to flinch the foe. It also hits Ground- and Fire-types such as Mudbray and Ponyta super effectively, both of which are OHKOed after a Shell Smash. Aqua Jet is a fairly powerful STAB priority move and allows Tirtouga to take out weakened threats and faster Choice Scarf users such as Mienfoo and Doduo, while also avoiding Sucker Punch and outspeeding other forms of priority such as Timburr's Mach Punch after a Shell Smash. Stone Edge is a STAB move that hits Flying-types super effectively, OHKOing Rufflet even without a boost and Vullaby after one Shell Smash, and it also deals significant damage to Grass-types such as Pumpkaboo-XL, which is 2HKOed after a boost, and Cottonee, which is OHKOed after a boost. Stealth Rock can be used over Stone Edge, as Eviolite makes Tirtouga bulky enough to set up Stealth Rock and come back in later to sweep; however, the lack of Stone Edge leaves Tirtouga more easily walled by Pokemon such as Pumpkaboo-XL and Vullaby. Zen Headbutt can be used to hit Fighting- and Poison-types super effectively, as it usually OHKOes bulky Mienfoo, Foongus, and Mareanie after a Shell Smash and Stealth Rock damage, and Timburr after a Shell Smash and a bit of prior damage, as long as Tirtouga has an Adamant nature. Earthquake is an option to hit Pawniard, Chinchou, and Mareanie super effectively, OHKOing all of them after a Shell Smash.
Set Details
Thanks to Solid Rock, Tirtouga can set up on some Pokemon that hit it super effectively like Mienfoo and physical Croagunk variants, while also allowing it to take certain priority moves like Mach Punch better. The given defensive investment along with with Solid Rock and Eviolite maximizes Tirtouga's bulk while sacrificing negligible power, especially after a boost. In particular, it usually allows Tirtouga to avoid the 2HKO from Croagunk's Vacuum Wave. 180 Speed EVs give Tirtouga 11 Speed, allowing it to outspeed the entire unboosted metagame after a Shell Smash. It also allows Tirtouga to outspeed 14 Speed Choice Scarf users such as Mudbray and Modest Magnemite, while Speed tying with 15 Speed Choice Scarf users like Timid Magnemite and Adamant Bunnelby after a boost. 132 Attack EVs significantly increase Tirtouga's Attack, making it deal as much damage as possible. A Jolly nature can be used to outspeed 14 and 15 Speed Choice Scarf users and Speed tie with 16 Speed Choice Scarf users after a Shell Smash. An Adamant nature can be used to OHKO certain Fighting- and Poison-types such as bulky Mienfoo, Foongus, and Mareanie after Stealth Rock damage and a Shell Smash boost with Zen Headbutt, but these OHKOs can also be secured if Tirtouga's team can use Knock Off to remove the Eviolites of the aforementioned Pokemon.
Usage Tips
Early-and mid-game, this Tirtouga set can be used to check Fire- and Flying-types, as its good bulk allows it to retain enough HP to attempt a late-game sweep. Still, you should focus on eventually setting up a Shell Smash. In addition to Fire- and Flying-types, this Tirtouga set can also set up on some traditional Tirtouga checks, such as Mienfoo and physical attacking Croagunk, thanks to Solid Rock. However, this is usually not recommended, as Tirtouga will still take significant damage from them, making it easier to be revenge killed by fast Choice Scarf users and priority users. Before setting up, opposing priority users such as Timburr and Pawniard should be removed, as they can easily stop Tirtouga's sweep. Despite Solid Rock, Tirtouga still has to be very careful of Grass-type moves.
Team Options
This Tirtouga set really appreciates Memento support, as it will not take much damage on the turn it sets up thanks to the offensive drops from Memento and its good bulk. Due to the lack of recovery on this set Memento support might keep it out of range of certain priority moves, such as Croagunk's Vacuum Wave. Cottonee is especially good as a Memento user, as it also has excellent defensive synergy with Tirtouga. Z-Memento also synergizes nicely with this Tirtouga, as it allows it to play much more freely early-game and makes it less susceptibleto being worn down, before being healed back up to full HP and attempting a sweep late-game. Diglett and Alolan Grimer can also provide Tirtouga with Memento support, though they don't synergize with Tirtouga as well. Aurora Veil support from Alolan Vulpix is appreciated for similar reasons to Memento support, though it persists even after an opponent switches out. Unfortunately the hail that Alolan Vulpix sets up can wear down Tirtouga somewhat. Drilbur is also a good partner for Tirtouga, as it can take on the Electric-types that threaten Tirtouga, set up Stealth Rock to help secure crucial KOs for Tirtouga, and remove entry hazards to improve Tirtouga's longevity. Flying-types such as Vullaby, Doduo, and Rufflet help Tirtouga by dealing with Grass- and Fighting-types. They can also carry coverage to hit Ferroseed, which completely walls Tirtouga. Another powerful Water-type such as Staryu or Corphish can synergize offensively with Tirtouga, as the two can weaken each other's checks, such as Ferroseed or Pumpkaboo-XL, allowing for a potential sweep by one of them. Staryu can also remove entry hazards for Tirtouga, increasing its longevity. Knock Off users work very well with this set, as they can remove Eviolites from defensive Pokemon, helping Tirtouga secure crucial KOs, especially on Fighting- and Poison-types such as bulky Mienfoo, Foongus, and Mareanie. For this reason, Pawniard works well to lure in Fighting-types and use Knock Off to remove their item, while Fighting-types such as Mienfoo and Timburr can lure in the aforementioned Poison-types. Fire-types such as Ponyta are also very useful, since they can check Grass-types for Tirtouga and have a much easier time breaking through Ferroseed than Flying-types do.