Advent Letty
Ice/SteelHP: 95
Atk: 115
Def: 110
SpA: 80
SpD: 80
Spe: 70
Ability: Advent
(Prevents secondary effects of attacks)OverviewHaving the combination of dual STAB priority, Swords Dance and 115 Base Attack makes Advent Letty to a fearsome late-game cleaner. Furthermore, she has solid coverage options to deal with resistors quite well. Advent is somewhat useful, since it prevents some parahax and flinches. The winter lady has some notable flaws, though - she's x4 weak to Fire, and being mainly just a physical attacker, a burn will make her dead weight. Keep her away from the heat, and she'll become a great asset.
Swords DanceEVs: 252 Atk / 252 HP / 4 SpD
Nature: Adamant
Item: Lum Berry / Maid Outfit / Thick Fur
-Swords Dance
-Ice Shard / Extremespeed
-Blade Flash / Extremespeed
-Earthquake / Poison Jab / Waterfall
This set is for finishing off a weakened team - having a solid physical bulk and resistance to most priority, she can switch into a crippled foe, set up Swords Dance and begin to sweep. Ice Shard and Blade Flash are your primary STAB options, though Extremespeed can be used if you don't need a Super-Effective hit, since it is stronger than both. The last move deals with her main threats - Earthquake helps against Fire-Types and Poison Jab against Water-Types. Waterfall can be used against Rin and Utsuho forms, but is otherwise outclassed by Earthquake.
ChoiceEVs: 252 Atk / 252 HP / 4 SpD
Nature: Adamant
Item: Special Bloomers
-Ice Punch
-Braver
-Ice Shard / Blade Flash / Extremespeed
-Earthquake / Waterfall
This set is dedicated to break down walls, as the item gives her a better immediate power than setting up Swords Dance. Ice Punch and Braver are for STAB, while the priority move should be selected to counter certain threats to your team. Earthquake is preferred as a coverage move as it catches Fire-Types off guard and helps against bulky Miasma-Types. Waterfall is again listed since it checks Rin and hits Earth-Types.
Double DanceEVs: 252 Atk / 148 HP / 108 Spe
Nature: Adamant
Item: Lum Berry / Maid Outfit / Thick Fur
-Swords Dance
-Agility
-Ice Punch / Earthquake
-Braver / Earthquake
This set forgoes a third attacking move in order to be usable as wallbreaker or late-game sweeper - depending on the situation, use Swords Dance against stall teams or Agility against more offensive ones, then start hitting things. The given EVs allow you to always outspeed Advent Marisa after an Agility - if you allocate 132 Speed EVs instead (take points away from HP), you'll hit 418 Speed, enough to outspeed Lily Black and Mimi-Chan (you need Earthquake to threaten the latter).
Other OptionsAdvent Letty can set up Spikes, so if you don't need her to attack, you can do that if need be. A pure Agility set might sound good, but Advent Cirno reaches enough Speed after one Tailwind, hits harder and has a better STAB in Ice Ball. Curse is an alternate set-up move, but the extra defense is often redunant and Swords Dance gets her attack up faster. When it comes to more coverage moves, Body Slam is the most notable example, since it can spread Paralysis. Alternately, Selfdestruct can break walls on the Swords Dance set to break walls or to finish with a bang on the Double Dance one, but it's hard to find a moveslot for it. Most others don't have worthwhile coverage, though. Also, she has a surprisingly wide array of special moves, but her Special Attack isn't that great - Surf might work if you're scared of Mokou burning you with Flame Body, but that's it. Lastly, if you like gimmick sets, you can use the combination of Block and Screech to set up a Pursuit trapping, but since she can already hit Dream- and Reason-Types well enough, this is pointless.
Checks and CountersThe biggest problem for Advent Letty is Defense Hina - she shrugs off most of her attacks and can either burn her or KO with Flamethrower/Fire Blast. Defensive sets of Rin check Advent Letty if she doesn't carry Waterfall - Intimidate will weaken her blows and she can then cripple her with Will-O-Wisp (beware of Lum Berries). Yoshika can also take a lot of her hits and do the same, but must be wary of Earthquake. Offensively, fast Fire-Types, mainly special-based ones, can scare her out with Flamethrower and Fire Blast - Attack Patchouli and Kisume in particular x4 resist her STAB combination. They both have to be careful about Earthquake, though. Lastly, Rock Bullet and Mach Punch can be employed against her, but with her high bulk, she can survive one at full health.
