The living embodiment of a paper cut turned up to 11 returns to terrorize once again. While Rillaboom is the de facto Grass type thanks to Grassy Glide + Grassy Surge being so strong, Kartana continues to prove why the Grass-Steel type combination is so strong... while having Attack ever higher than Attack Deoxys with built-in Moxie. Unfortunately (or thankfully) Kartana does not get Grassy Glide, depriving it of a powerful priority move. However with 109 Speed, Kartana still outspeeds huge swaths of the game, making it a simple chore to pick up KOs and escalate to an unmanageable level quickly.
However, not all is good for our wanna-be Origami. Kartana's ludicrously bad Special Defense ensures that even resisted special attacks will do serious damage. An poor HP means that even that amazing Defense won't save Kartana for long. Additionally the addition of a new naturally faster Special threats in the form of Regieleki and Dragapult puts more pressure on Kartana to shoehorn to Choice Scarf which can leave Kartana prone to being walled out by the standard walls in the format. Additionally, Kartana's movepool is rather small, leaving it rather predictable. In the end though, Kartana remains an insanely powerful threat that must be fought with care lest it cut your team in twain.
The Dual Bladed Duelist
Kartana
Ability: Beast Boost
Item: Protective Pads/Life Orb
-Swords Dance
-Leaf Blade
-Knock Off
-Sacred Sword
EVs: 252 ATK / 4 SDEF / 252 SPE
Nature: Jolly (+SPE, -SATK)
Yes I couldn't resist the Origami King reference. Swords Dance Kartana is a potent win condition with a single Swords Dance enabling Kartana to blow past checks that would normally wall it out:
+2 252 Atk Life Orb Kartana Knock Off (97.5 BP) vs. 252 HP / 168+ Def Corviknight: 264-311 (66 - 77.7%) -- guaranteed 2HKO (needs to Roost to avoid being KO'd by Sacred Sword)
+2 252 Atk Life Orb Kartana Knock Off (97.5 BP) vs. 252 HP / 252+ Def Skarmory: 200-237 (59.8 - 70.9%) -- guaranteed 2HKO (needs to Roost to avoid being KO'd by Sacred Sword)
+2 252 Atk Kartana Knock Off (97.5 BP) vs. 248 HP / 8 Def Volcarona: 381-449 (102.1 - 120.3%) -- guaranteed OHKO
Leaf Blade is for STAB, while Knock Off and Sacred Sword provide the best coverage of all of Kartana's moves. EVs are standard sweeper array. Item is where it gets interesting. While Life Orb is standard, Protective Pads protects against predicted Flame Body Volcarona and Moltres whose unlucky burns can end a sweep before it starts, while preventing numerous Rocky Helmet/Garchomp/Ferrothorn's from wearing down Kartana via their item/ability.
Team Support is required as Kartana needs allies to provide opportunities to setup and remove or weaken potential checks and counters.
Other Options
Smart Strike -Alternative STAB option, but Steel has much poorer coverage than Grass and the few Fairies that actually have good DEF are neutral to Steel Strike (admittedly, Togekiss is a problem that is covered by Steel Strike)
Psycho Cut -Alternative Coverage option, but the popular fighting types are either Weak/Vulnerable to Leaf Blade/Sacred Sword, naturally Faster than Kartana, or have access to STAB priority.
Aerial Ace -Turns into a Max Airstream in Dynamax format and can combine with Sacred Sword for a Vicious Dynamax setup Sweeper.
Defog -Kartana gets it and isn't weak to Ice or Electric moves (though still doesn't want to take special hits)