When the special button is pressed, K. Rool pulls out a blunderbuss and shoots a Kannonball forward, donning the pirate hat he used in Donkey Kong Country 2: Diddy's Kong Quest. The projectile is slow, travels straight for 3/4 the length of Final Destination and deals 13%, with relatively strong knockback, being able to KO around 130-150%. After around 2 seconds, the Kannonball will disappear. K. Rool cannot fire another Kannonball if the one he previously shot is still in play, instead firing a "Fake Shot". The Fake Shot will simply have smoke come out, being almost completely useless and leaving K. Rool vulnerable until the move ends.
If the special button is held until Frame 25 while the Kannonball is in play, the Blunderbuss will suck in air in front of K. Rool, creating a vortex which also acts as a command grab. This takes an additional 6 frames, making it Frame 31. This can also be done directly after firing the Kannonball as well, although it takes slightly longer. The Blunderbuss will continue to suck as long as the special button is held, for a maximum of 2.5 seconds. K. Rool can drop through platforms while in this state, and while dropping a player can influence the trajectory as well. If the player's own Kannonball or an opponent comes near the vacuum, the Blunderbuss will trap them inside it and K. Rool shoots them out immediately afterwards, acting as a command grab. However, it will usually prioritize a player rather than the Kannonball. While an opponent or Kannonball is being sucked in, K. Rool can still fall through platforms, enabling more unique reshoots. This also allows K. Rool to carry Kannonballs around, maintaining their hitbox. If a Kannonball is reflected, it can still be sucked in as well, returning ownership to K. Rool. However, other player's Kannonballs or projectiles cannot be reshot.
If a Kannonball hits a wall or player, it will fall down and retain its hitbox until it hits the floor, in which case it disappears after around half a second. This means that one can shoot an opponent with a Kannonball, drop down while vacuuming, and still manage to reshoot it. However, the length of time the Kannonball is out makes the practicality of this strategy questionable. Off-stage, a falling Kannonball can be used to disrupt recovery, or a bold player could reshoot it at the opponent for a stylish KO.
If a Kannonball or player is sucked into the Blunderbuss, K. Rool can pick the direction they're shot out. The shot can be aimed in 3 directions; up and forward, directly up or backwards, and this can be inputted from Frames 16-21. Due to this, it is possible to delay a Reshoot by a few frames, although utility is questionable. Forward Reshoot is a very strong throw, KOing opponents at around 120% at the edge. Upward Reshoot is niche but can be used to set up for up aerial as a frame trap, or for KOs at the top platforms of stages like Battlefield. Backward Reshoot is useful when recovering while using Vacuum after being launched high, as K. Rool can carry opponents to the blast zone they were trying to send him to. This either closes out a stock early or ends in a stock trade (K. Rool will be KO'd first). Due to this, opponents will be less inclined to try and stop K. Rool from returning.
If a Kannonball is sucked in, it will be reshot. When this occurs, its damage increases to 17% with noticeably higher knockback. It is considered a new projectile by the game (known as "spitball" rather than "ironball", meaning that no matter how much a Kannonball is reflected, if it is reshot it will return to the default damage. Once shot out, however, reflectors can increase the damage of the reshot Kannonball as usual, although reshooting it again will return it back to normal. Reshot Kannonballs will remain until they reach the blast zone.
If an opponent is shot out however, the reshoot will inflict 12% damage to said opponent and briefly turn them into a projectile. During this state, the opponent is intangible, somewhat limiting combo utility. Furthermore, opponents that are reshot cannot be reflected. While primarily useful in free for all and team matches, his also helps K. Rool against the Ice Climbers and Rosalina & Luma, as he can potentially hit their partner while reshooting.
In the 6.0.0 update of Ultimate, Blunderbuss received a rework to how Reshooting worked. All Blunderbuss throws and reshoots were made faster (interestingly, reshoots no longer match the animation), and Vacuum also had a searchbox added for the Vacuum feature when sucking up Kannonballs. This is designed to make taking in Kannonballs easier, thus allowing for Kannonball reshoots to be much more consistent. Prior to this, the vacuum's grabbox and windbox were used to pull Kannonballs in. This new searchbox allows for more flexibility when taking in Kannonballs, allowing for them to be sucked in from quite far away and even be carried off-stage. During this situation, the Kannonballs also retain a hitbox, enabling confirms from a ricochet hitbox into a reshot Kannonball. It is also far easier to suck in Kannonballs from platforms due to the sheer range of the searchbox. It can also allow for Kannonballs to be sucked in from off-stage while K. Rool is at the ledge, enabling a method of dealing with opponents recovering from high up. As a result, the new Blunderbuss vacuum searchbox patched up a lot of flaws reshooting as a strategy had, allowing for more creative use of the move.
Blunderbuss Vacuum Delay
Though holding the B Button will transition Blunderbuss into the Vacuum stance, this isn't actually the only way to do it. By tapping B to trigger Blunderbuss, there are 19 frames (after the shot) where Vacuum can be inputted at any point. This is known as Blunderbuss Vacuum Delay by the playerbase.
This tech is typically used by King K. Rool players when ledgetrapping, as a mixup. For example, a player seeking to end a ledgetrap situation quickly could try to jump and attack, only to get caught by a delayed Vacuum to reset the recovery situation again. In circumstances where this catches a jumping opponent (for example trying to use a forward aerial after being knocked back only slightly), this can potentially gimp them. It can be used when dropping through platforms in a similar manner, minimizing the potential punish for not using it far away.
Managing Vacuum Delay isn't too difficult, although practice in Training Mode can help a player understand the timing for catching opponents. As a general rule, Vacuum has 6 Frames of startup, meaning it is very possible to catch opponents on reaction. As a result, this tech is extremely practical when one is attempting to zone and keep the opponent out: it doesn't have to be executed with intention, it can also be executed as a defensive measure.
Fake Shot Vacuum Cancel
In a similar fashion, while the Blunderbuss's Kannonball is out, the move actually changes completely. The "Fake Shot" - where the Blunderbuss shoots but nothing comes out - actually can be cancelled into Vacuum at any point after Frame 25. This is known as a Fake Shot Vacuum Cancel, and is simply executed by pressing and holding B during the Fake Shot animation. The reason this occurs is unknown, though players assume it is because holding Vacuum is actually buffering it to happen on the first possible frame.
Executing this, while simple, allows for a good degree of creativity in the bait and punish playstyle. Given Fake Shot can be cancelled even as the Blunderbuss is "shooting", it's possible to "camouflage" the tech through the smoke. As a result it's possible to deceive players during the match and manage to get more reshoots off than normal and continue playing mindgames with the opponent. As a result, there is extremely large mixup potential resulting from this. That is, if the player doesn't figure it out.
This works best on opponents being too aggressive and trigger-happy on their punishes, allowing the King K. Rool player to easily reset neutral and press his neutral-based playstyle further. The best movement setup for this is dropping through platforms and suddenly going into Vacuum when the opponent tries to exploit the Blunderbuss's lag. This is because players can typically intercept poor platform movement in other matchups anyway, making it very strong bait. It is also used when ledgetrapping as a red herring to keep the mindgames going, though typically Vacuum Delay is better for this. Overall, this isn't inherently useful, but adds to K. Rool's endless bag of tricks.
This attack is based on the boss fight against Kaptain K. Rool, King K. Rool's pirate persona, in Donkey Kong Country 2: Diddy's Kong Quest. In the fight, Diddy Kong and Dixie Kong have to avoid Kannonballs shot by K. Rool, then grab and throw them into his blunderbuss when he tries to vacuum up the Kongs; if a Kong got close to the blunderbuss as it vacuumed, they would not get sucked inside, but instead K. Rool would strike them with the butt of the gun. Throwing a Kannonball into the blunderbuss as it vacuumed would result in it clogging up and exploding, dealing damage to K. Rool in a comical manner; this also shoots the Kannonball back out at increasing speeds as the fight goes on. Kannonballs also bounce one as they hit the ground, similar to how they did in Donkey Kong Country during the boss fight against King K. Rool.
Unlike in Ultimate, Kaptain K. Rool's blunderbuss could shoot out Kannonballs with spikes, and at various heights and trajectories, such as bouncing on the ground or spiraling through the air. It could also be used to rocket K. Rool across the stage, with the blunderbuss acting as an exhaust. It could shoot odd mists that would freeze, confuse or slow down Diddy and Dixie Kong on contact. The explosion is also absent, likely due to not wanting the move to inflict damage on the player, especially considering the ease at which a cannonball can be regained.