Persona 5’s Brutal Cavalryman, known as Berith once you discover his true name, is one of the hardest regular enemies you will face in Kamoshida’s Palace. On most difficulties, Berith can wipe out your entire squad if you are not careful. He seems to have a fairly high critical rating, meaning that he will get the "1 more" bonus frequently. Lucky for you, he does have a weakness.
As you can see from the tactical guide above, Ann’s fire spells and your gun won’t help you much here. However, if you have a Persona with any Ice skills, you will be able to take down Berith fairly easily. If you capture the Persona Silky, the enemy maiden with green hair, she will come with Bufu, a low-level ice spell.
Use Joker’s ability to Persona swap to your advantage and take Berith down with Ice moves. Berith does show up frequently, so acquiring an Ice move early on will be critical to your success in this palace. If you are low on SP, guarding regularly with Morgana and Joker so that they survive is another decent tactic. If you can take Berith out quickly with strong attacks, it will be harder for him to combo you. Good luck!