Shoot / Lock
Shooting and/or Locking is a skill that's part of the player's moveset. Shooting is one of the absolutely necessary, core mechanics responsible for the player making progress in the game. Holding down the respective lock button will allow the player to aim in one of eight directions while shooting, though ducking or running cannot be done during this. Shooting, as the name would imply, is the act of firing a projectile with the intent to do damage, therefore defeating enemies and bosses. By default, the player is given the Peashooter, the most basic weapon in the game.
Shooting can be customized by purchasing and equipping different types of weapons or "shots". Note that each kind of weapon is meant to act as a side grade to the Peashooter with their own unique pros and cons, and act differently when fired, which effectively changes up the player's strategy when using them. Because of that, different weapons work more efficiently for different bosses. Coins in the game are limited, so the player may not be able to purchase every type of weapon. Therefore, purchases should be planned out carefully.
Charms can also affect how a weapon works. For example, equipping the Twin Heart charm will grant the player with two extra hit points, but at the cost of reducing weapon damage by 10%. As mentioned before, different weapons fire different and each have unique trajectories and firing patterns. For example, the Lobber does more damage than the Peashooter, but the projectile is heavy and fires in a downward arc and bounces along the ground, which is helpful when firing straight ahead or down, but presents an issue when trying to fire upward, so the player must jump to try and counteract this.
In another example, the Roundabout also does more damage than the Peashooter, but the projectile has limited forward range, as it will slow down and accelerate the other way, meaning the player must either stay close to their target, or just fire it the other way. Lastly, in this final example, the Chaser completely negates the need to aim at all, as the projectiles will slowly, automatically home in on the target. However, the downside is that the projectile's damage is lower than that of the Peashooter. Another downside to Chaser is that projectiles hone in on the closest target, meaning that the projectiles may travel to unintended targets, making combat trickier.
When playing as an airplane, the player can shoot mini-missiles, which act as the default projectile weapon. When speaking to Canteen Hughes for the first time in Inkwell Isle One, the airplane will be fitted with bombs that can be lobbed, which do more damage than the missiles, but have a slower rate of fire with a heavy downward arc as tradeoffs. These two firing modes are the plane's only modes of fire, and can not be customized as if the player was playing on the ground. However, some charms (like Heart and Twin Heart) can still affect weapon damage.
When playing as Ms. Chalice by using the Astral Cookie, there are unique differences to her projectile firing behavior. When she fires the standard Peashooter, her rate of firing is slightly slower, but there is a very slight spread among the projectiles. As an airplane, her mini-missiles do not fire in a straight line, but instead fire in an outward cone-line fashion - meaning that Chalice must get closer to enemies for all missiles to make contact. Also, her bomb lob fires at a faster rate than Cuphead's/Mugman's, and also has more of a randomized, "spilling" spread.
Though this is never explicably stated, when observing the properties of other weapons, the damage will almost always use the Peashooter's damage as a reference point.