Pressing the special button causes Joker to fire his gun once, and he will continually fire if the special button is pressed multiple times. Holding the special button down also causes him to continually fire the gun, but the rate of fire will not be as fast as it can be with repeated presses.
On the ground, Gun has various options:
All of this functionality is retained if the gun is used in the air, and Joker also gains two new options. However, Joker cannot jump out of Gun, instead needing to end the move before jumping.
Additionally, the Gun stalls Joker in the air when used, which can be used in conjunction with a double jump to let him go under stages like Battlefield. Outside of this, the aerial Gun dodges can be used to recover horizontally in certain situations, which can easily be boosted in viability with Arsene.
If Arsene is present, the attack is upgraded to Gun Special (ガンスぺシャル, Gun Special), and Joker will fire three bullets with each shot when firing straight forwards. The other two methods of firing become stronger, as well. The "bullets" have increased knockback values as well, making them much more favorable for forcing tech situations. The damage is also quite high and racks up quickly, allowing for Joker to force approaches effectively in a way similar to Fox's Blaster.
Much like Bayonetta's Bullet Arts, the bullets are not projectiles, but rather indirect attacks with large disjointed hitboxes. As such, they cannot be reflected or blocked by passive shields. Unlike Bullet Arts, these bullets can actually cause flinching. Due to this, they can force Counter attacks to trigger, allowing for some interesting offensive pressure.
There's a unique tech with Joker's Gun which involves landing while executing a forward or backward dodge with it. This is known as a Gundash. Through this, Joker will slide a long distance, akin to a wavedash. The distance of a Gundash can vary, mainly depending on the player's timing. The later the dodge is performed, the longer the dash will be, just like how Wavedashing works.
The applications with this are somewhat limited due to how long it takes to pull off, but it's very useful when executed in the right circumstances. For example, it can be used in a way akin to a ledgedash would be in Melee, allowing for Joker to have increased options to use if he's being oppressed on the ledge. On the flip side, Gundashing to the ledge is also very possible to set up for an edgeguard. Gundashing close to the ledge and then using the Jump option to rain bullets on the opponent for a gimp is also a very powerful option in this respect.
Outside of setting up for ledge options, Gundashing can also be used to press advantage by using its properties to slide while using attacks or increase Joker's general speed even further. Holding B will keep Joker using the Gun, meaning all the options it provides are also still available. As a result, Gundashing close and using another Bullet can potentially set up for a tech situation or perform a lock.
Firearms are a class of weapon used in several Megami Tensei games, including every main game in the Persona series. In Revelations: Persona and Persona 5, all party members carry both a melee weapon and a firearm they can switch between in battle. In Persona 5, party members can pull out their gun during their turn in a battle and fire it as many times as they wish until the current magazine runs out. In the original release of Persona 5, guns have a limited supply of ammunition that cannot be restored without either using rare items or leaving the current dungeon. In the rerelease Persona 5 Royal, ammo is replenished at the end of every fight.
Joker uses semi-automatic pistols, while the other members of the Phantom Thieves use different types of firearms. While they are actually realistic models and not genuine guns, the nature of the Metaverse allows them to function as if they were real. The gun Joker uses in Smash Bros. is his initial gun in Persona 5. Referred to in-game as the Tkachev, it is based off the Type 54, a Chinese copy of the Tokarev TT-33.
Joker's acrobatic maneuvers when using Gun is likely a reference to the Down Shot special attack he can learn from Confidant Oda Shinya, an elementary schooler who is a light gun game prodigy. The animation for Down Shot shows Joker gracefully dodging and leaping into the air while firing at the enemy.
Gun Special may serve as a reference to Snipe and Cripple, two skills Personas can learn in Persona 5. Snipe and Cripple both passively boost the damage of all gun attacks. Arsene does not learn either normally, but he can be taught them via Fusion or Skill Cards. Gun Special may also reference other elements of skills that Joker can learn from Shinya. Down Shot shows Joker firing his gun in three-round bursts, downing the enemy. Upon reaching Rank 10 of the Confidant, Joker learns the Oda Special, a skill that allows his bullets to ignore an enemy's resistances. It could also be a reference to the skill Triple Down, which hits all enemies with gun damage three times.
The bullets being treated as a physical attack instead of a reflectable projectile is possibly a reference to them being treated as physical attacks in Persona 5. This is further implied by them activating Tetrakarn rather than Makarakarn on another Joker, just as in the original game.