After defeating the Elite Four and finishing the main storyline, you will be able to start battling and catching the Ultra Beasts through the Looker Storyline. The fourth Ultra Beast you are set to capture is Kartana. Like all Ultra Beasts, Kartana has some pretty incredible Stats. It's more of a Physical Sweeper, with extremely high stats in both Attack and Speed. Luckily it's only a Grass/Steel Type, allowing it to be paralyzed.
Here Are Some Tips For Catching Kartana:
Like many of the other Ultra Beasts, you are set to catch more than one Kartana, four to be exact. It can be found randomly on Route 17. Since it's at Level 60, a player can easily put a Level 60 Pokemon at the lead of their party and use a Repel to quickly find Kartana in this area. A player will know they are near this Ultra Beast by a change in the music and a not-so-far off cry from it.
Right as the Battle begins, Kartana's already impressive Attack will increase by two stages, making it a serious threat. The first thing you can do to limit it is by paralyzing it on the first turn in battle, almost guaranteeing your Pokemon will always move first and making it easier to capture. Fire Type Pokemon fair well against Kartana since it mainly uses Grass Type Attacks. From there, try to lower Kartana's HP as low as you possibly can. Moves like False Swipe and Hold Back work great when it has low HP, ensuring to leave at least one HP. The lower it's HP is, the better chance you have at catching it.
But keep track of the more Pokemon Kartana knocks out on your team, as its Highest Stat will increase every Time it does so because of its Beast Boost Ability. Because of this, like all the other Ultra Beasts, it's best to try to capture it as quickly as possible with the Beast Ball, since it has a x5 Catch Rate with Ultra Beasts. But don't be afraid to use Ultra Balls on Kartana, if you'd like to save your Beast Balls for your next challenge.
And don't forget to ALWAYS save before trying to find Kartana. It's a safety precaution, one that has worked since the first generation of Pokemon.