Fusion Alarms are a new feature in Persona 5 Royal that influence the many features of the Velvet Room. In addition to this, using the Velvet Room's electric chair to itemize a Persona will have a different result than itemizing without the alarm. Players should be cautioned of the Velvet Room during the alarms thanks to unpredictability.
During a first playthrough of Persona 5 Royal, players should take full advantage of the Fusion Alarms. They're ideal for getting ultimate weapons and Skill Cards - especially on NG+. The Fusion Alarms unlock after securing the Treasure Route in Kaneshiro's Palace. Unfortunately, their availability won't carry into NG+, meaning players will be locked off from the alarms until the third act of each new playthrough.
How To Get Fusion Alarms
The most well-known way of triggering Fusion Alarms is to defeat Shadows. Players can fight Shadows one by one, or they can use the help of Ryuji's Insta-Kill Confidant Ability (unlocked at Rank 7). To be specific, the Insta-Kill Ability, as its name indicates, will instantly kill a Shadow if Joker dashes into it. In addition, this nets him a new Persona (if he has room), EXP, money, and (occasionally) an item.
However, the Insta-Kill will only work on Shadows that are low-level (green auras). Joker can check a Shadow's "level" by using his Third Eye ability. In Mementos, Shadows with green auras will flee if players get too close. If a Shadow has a cyan, yellow, or red aura, it cannot be Insta-Killed.
To increase the chances of a Fusion Alarm, get Chihaya's Confidant (Fortune) to Rank 8. Following this, Joker can go to her for a special reading.
Players that need a Fusion Alarm immediately should go to the first floors of Mementos once they're a high enough level. Keep dashing into Shadows to insta-kill them, and players will have a Fusion Alarm in no time. They'll be able to tell a Fusion Alarm has occurred when the Velvet Room door flashes red on the screen. Joker will also mention that he's getting an "uneasy feeling." If players are in a Palace, Joker will remind players of the Fusion Alarm every time he enters a Safe Room. The Fusion Alarm will disappear if Joker leaves the Palace/Mementos.
What Happens During Alarms?
Players just looking to get a Persona from the Registry can ignore the alarms and simply get what needs to be done. The Twin Wardens will remind Joker of the alarm if he tries to leave, since leaving will deactivate the Fusion Alarm. In short, Fusion Alarms changes or doubles the effects of all Velvet Room features. The following categories are influenced by Fusion Alarms: Persona Fusion, Sacrificing Personas, Itemizing Personas, and Training.
Guillotine (Fusion) And Sacrificing Personas
Using the Guillotine is how Joker can fuse new or stronger Personas while carrying over some Skills and a Trait. Each time a Persona is fused, it gains a boost in EXP. Initiating a Fusion during an alarm will double the experience gained, and also has a chance of "Changing" a newly-Fused Persona's Skills. For example, the Skill will be written in red letters and start to "shake." Igor will then ask if Joker wants to change the Skill into something else.
Unfortunately, the Skill transformation is completely random. Depending on the Persona's stats, a good Skill can turn into something useless. A Physical-fighting Persona won't have much use from the Skill Concentrate (which doubles the next Magic attack). Players should look at the stats of the newly-fused Persona and see if the confirming the Skill Change is worth the trouble.
Get Caroline and Justine's (Strength) Confidant to Rank 1 to unlock the Group Guillotine. This allows Joker to fuse more than two Personas. Some Personas can only be obtained through a Group Guillotine, so it's important to help out the Twin Wardens to get these features as soon as possible.
Another feature worth using is Persona Sacrifice. This will sacrifice one of the Personas in Joker's roster to strengthen another Persona (in the roster, of course). Doing so won't transfer Skills, but it's a quick way to level upPersonas without having to EXP grind. Sacrificing a Persona during a Fusion Alarm will greatly increase the EXP of the Persona that players are trying to level up.
Electric Chair (Itemization)
Once players unlock the Velvet Room's Electric Chair, they'll be able to turn one of their Persona (in the roster) into an item. This can be a Skill Card, Accessory, Protector, or Weapon. When a Fusion Alarm is active, the item that a Persona normally can turn into will be different. For example: Haru's Ultimate Weapon, Fleurs du Mal, is itemized from the Ultimate Persona: Beelzebub. However, if Beelzebub is itemized during a Fusion Alarm, the Fleurs du Mal will instead read Fleurs du Mal R, which is a stronger version of the regular Fleurs du Mal.
Getting each Phantom Thieves' Ultimate Weapons in Royal requires the use of the Electric Chair during a Fusion Alarm.
When itemizing a Persona into a weapon, accessory, or protector, players will need a Black Kogatama, Black Rock, or Black Robe respectively. These can be bought from the street vendor on Central Street once Joker has reached Level 5 Charm. Fortunately, they can also be obtained from Jose in Mementos, or stolen from Shadows.
Lockdown (Training)
Lockdown is a feature that unlocks once players have reached Rank 3 of the Strenght Confidant. While advancing through Persona 5 Royal's campaign, players may have picked up "Incense" items. These can be bought at the Incense Shop in Kichijoji (in the alley across from the Darts Lounge). Alternatively, players can get incense by giving Jose a set amount of Mementos Flowers.
There are several categories of incense that increase one (or more) of a Persona's five stats. To use an incense, go into the Velvet Room and select Lockdown. Players will then be prompted to choose a Persona from their roster. After selecting one, Caroline will ask if Joker wants to light any incense. During a Fusion Alarm, the incense's effects will double. Thus, using Lockdown while a Fusion Alarm is active is ideal for raising a Persona's stats.
Keep in mind that a Persona in Lockdown can't be used in battle until Joker goes to bail them out. Also, Personas that are not picked up within a certain timeframe will disappear. Caroline will contact Joker with a warning to get the Lockdown Persona.
Using The Alarm More Than Once
Players would do well to remember not to be greedy when using the Fusion Alarm. Trying to Fuse more than one Persona during an alarm has a high risk of a Fusion Accident, which occurs when the Persona that Joker is trying to create, instead turns into something else. However, each of the Velvet Room features can be used once during a Fusion Alarm with high success.
After that, players will receive a warning about the guillotine or electric chair. Choosing to ignore it will have expected results. If players are using Fusion Alarms to get Ultimate Weapons, they should itemize the required Persona for one weapon, leave, and then trigger another alarm.
Persona 5 Royal is available now on PS4, PS5, Xbox Series X/S, Nintendo Switch, and PC.