During the boss fight against Masayoshi Shido, Shido claims that he was "chosen by God" to lead the people of Japan. As it turns out, he was right, but then the god who chose him is evil. Thus, in the grand JRPG tradition, the final boss of Persona 5 Royal is the divine being known as the Holy Grail.
To reach the Holy Grail, players of Persona 5 Royal must reach the very heart of Mementos. That's where the Treasure of the general public is hiding, and the Holy Grail will reveal itself to be both the result of human desires and the one who's causing those desires to spiral out of control. The first part of the boss fight begins when the Phantom Thieves finish descending into the Mementos Depths.
A Tarnished Cup
This phase of the fight is easy. During the first round, players can use any attacks they like on the Holy Grail, and it'll respond with Will of the People, a special skill that lets it heal several thousand HP at once.
After a cutscene, the fight will begin again. The Holy Grail will attack using Arrow of Light, which targets one party member and hits them with colossal Almighty damage. However, if the Grail loses enough HP, it'll use Will of the People on its turn instead. This can seem to make attacking the Grail pointless, but after it uses Will of the People three times the Grail will regain its golden shine and the fight will end.
A Glorious Rematch
Assuming players don't accept the evil god's deal, the Phantom Thieves will get a rematch against the Holy Grail after traversing the Qliphoth World. The red veins feeding into the Grail are still a problem, though, and so this battle begins with Joker getting a chance to order a party member to sneak around and cut them off.
Much like the first fight with Kamoshida's Shadow, players will need to deal damage to the Grail each round to keep it from spotting the sneaking party member. Unlike with Kamoshida, players can send any Phantom Thief to do the job. After two rounds of combat, the party member will cut through the veins and the Holy Grail will be unable to use Will of the People to heal.
Aside from the healing gimmick, the Holy Grail has no elemental affinities and no elemental attacks. Instead, all its attacks deal Almighty damage. Arrow of Light is back from the first encounter, and Diffraction Arrow will target random party members with a chance to cause Forget. Then there's Light Edge, which can hit the whole party. All these attacks deal serious amounts of damage, but the Holy Grail only gets one action per round.
The Grail's super move is Eternal Light, which deals even more damage than Light Edge. It spends a round preparing for this move by using Gathering Light, so have the party guard to avoid the worst of the damage.
Yaldabaoth
When players defeat the Holy Grail, it will reveal its true form: Yaldabaoth, the God of Control. In Gnostic sects, Yaldabaoth is considered to be the evil god or Demiurge who created the material world as a way to distract humans from the true spiritual world. The Demiurge has shown up in other Shin Megami Tensei works, but this is his first appearance in the Persona series.
Players should first note that any HP or SP used up during the Holy Grail fight is still missing, so a good first action during the Yaldabaoth fight is to use a Soma and get everything back.
Yaldabaoth only gets one action per round, and for the most part, he uses them on Arrow of Light, Dekaja to clear party buffs, and Dekunda to clear debuffs. However, he can also summon up to four arms, and if players don't take them out quickly, each arm will get its own set of actions. This means Yaldabaoth can act up to five times per round, and the arms add a lot of variety to his move set.
The first arm is the Gun of Execution. When Yaldabaoth summons it, it will use either Distorted Lust or Distorted Avarice. Distorted Lust will hit a party member with a little damage and the ailment Lust, which can force them to lose a turn (it works identically to Fear, but it can't be cured by most normal items or skills). Distorted Avarice causes damage and the Hunger ailment, which is much easier to cure. If the Gun of Execution gets a chance to take its own actions, it will use Capital Punishment to deal a lot of damage to one target or Shoot Up to hit three random party members. The Gun can also repel both Gun and Wind elements.
The second arm is the Bell of Declaration, which represents Vanity or Envy. Distorted Vanity deals a lot of damage to one party member and increases their ailment susceptibility. Distorted Envy will inflict the Jealousy ailment, which causes the affected party member to attack another party member if they used a support skill or item on someone else. The Bell's actions include Gospel, a basic Almighty attack; Frail Law, a defense debuff that hits the party; and Tough Law, a defense buff for Yaldabaoth and every active arm. The Bell repels Fire and Psy damage.
The third arm is the Sword of Conviction, which only represents Gluttony. Distorted Gluttony hits the whole party, and while it's active, every skill will cost double in either SP or HP. The Sword can use the Sword of Judgment to hit every party member or Wind Cutter to hit just one. It can repel Physical, Gun, and Electricity damage.
The fourth and final arm is the Book of Commandments. The first time it appears, it'll use Distorted Wrath, which hits a target with the Wrath ailment. This works just like Berserk by boosting attack and lowering defense, but unlike Berserk players can still choose the party member's action. Its second appearance will activate Distorted Pride, which lets it hit any character who attacks it with Divine Punishment. This skill drains a target's SP by 15 percent of their total. The Book's normal actions include the single-target -dyne skills for every element, and it will tend to target elemental weaknesses. It also has a more generic attack called Wrath of God, and it can repel Ice and Nuke attacks.
Players should note that all the special ailments and conditions Yaldabaoth invokes with the Distorted skills last for only one round each, and they only trigger when he summons or resummons an arm. Also, while most items and skills won't work on special ailments, Harisen Recovery can.
Once Yaldabaoth drops to around one-third of his starting health, he'll manifest all four of his arms at full HP and use the skill Divine Apex. Two turns later, he'll use Rays of Control to deal extreme Almighty damage to the whole party. Players can use these turns to damage Yaldabaoth and his arms, and while destroying the arms will reduce the damage the Rays deal it won't stop the countdown. Yaldabaoth can repeat his super move as often as he likes, so players should hit the god as hard as they can once this cycle begins.
There's more to the fight after Yaldabaoth drops to zero HP, but it's all cinematic. The only thing players need to do after that is enjoy the ending (or else keep going into the third semester if it's unlocked).
Persona 5 Royal is available now on PC, PS4, PS5, Switch, Xbox One, and Xbox Series X/S.