Another late-game tip: if you use katanas, get the Sword of Execution mystic art the moment it’s available. I went for the “spend less Ki with a sword equipped” one instead and that was a big, fat waste of skill points. I barely noticed it.
Sword of Execution, though? Well, for one thing, you should already be doing everything you can to hit enemies in the back whenever possible, especially bosses. Sword of Execution seems to double the damage you do from behind on top of the boost you’re already getting. I went from doing 750-800 damage per swing from behind to 1500-1600 from behind. It’s insane. If I tag an NG+ boss with a Weakness Talisman, hit them with Discord (which we’ve established is pretty easy with a weapon buff + a guardian spirit of a different element and the Guardian Spirit Talisman), and then buff myself with Carnage, I can reliably do like 6000 damage per swing from behind. Even on NG+, that just makes things melt.
That said, the Weakness + Carnage + Discord thing is good advice from the moment you have access to the necessary talismans. Discord is hard to apply if you’re relying on weapon buffs but really easy with the Guardian Spirit Talisman, and when any boss is Discorded, you can stunlock them with light attacks just by mashing square. People talk about how the Sloth Talisman breaks the game, but that shit is amateur hour compared to this. It can help to Sloth the boss first just to give yourself extra breathing room to apply the necessary debuffs, but it’s not really necessary.
(If you’re worried about the defense debuff the Carnage Talisman puts on you, well, it does make you take double damage. If you do the Discord thing right you shouldn’t get hit anyway, but if you want to play it safer, use the ninjutsu Power Pill instead. It’s a weaker attack buff but doesn’t have any associated debuff.)