PK Thunder

PK Thunder (, PK Thunder) is the up special move for Ness and Lucas. The move creates a stream of lightning consisting of two parts: a circular "head" which is controlled by the player using the control stick or d-pad, and a "tail" which follows behind. As control stick and d-pad inputs are used to aim PK Thunder, Ness and Lucas are unable to move or defend while the move is active. PK Thunder can be aimed into opponents to deal damage with the head and stun with the tail.

Aiming the head into Ness and Lucas themselves will launch them in a trajectory opposite to the side they were hit on. This is referred to as PK Thunder Tackle or PK Thunder 2. PK Thunder 2 is Ness and Lucas's main method of recovery and will damage any opponents that come into contact with them while in this state.

Similarities
PK Thunder's head has a direction of knockback 90 degrees clockwise in relation to the direction it's moving. Each side can hit a shield safely without it disappearing, and due to hitbox renewal (the attack can only hit once every 48 frames) it is possible for the attack to safely go through shields. The tail cannot be cancelled.

Ness
Ness's version of PK Thunder has a more blueish coloring to it, and he hunches over when using it. The head of Ness's PK Thunder disappears upon contact with most attacks, walls, and characters. Impact deals 8% damage and knockback, and launches in the direction the opponent was hit, but can't launch downward.

In Super Smash Bros. Melee, PK Thunder does not disappear on contact with most attacks, as it is a laser projectile similar to Fox's blaster. In version 1.00 of Melee, an uncontrolled PK Thunder can hit opponents and Ness himself. This means the player can intentionally hit Ness with the tail of PK Thunder to block him from flying off the screen. This technique is called a PK Thunder Barrier. PK Thunder can also be used to perform the Electric Ness glitch, where sparks will continue to show around Ness even when PK Thunder is not active. This glitch serves no offensive or defensive purpose.

In Super Smash Bros. Brawl, PK Thunder turns in a tighter circle than previous games, meaning it can be used to recover in narrower spaces.

Lucas
Lucas's version of PK Thunder has a more vibrant purple tint to it, and he strikes a different pose than Ness when using it. Additionally, the head of Lucas's PK Thunder goes through enemies and some objects, allowing it to score multiple hits. Each impact deals 9 to 10% of damage. Compared to Ness in Brawl, Lucas's PK Thunder also moves more slowly, has a shorter tail which deals less stun, and turns in a tighter circle — the latter meaning it is more favourable for recovery in narrow spaces. In Super Smash Bros. 4, its ending lag is also much higher when used on the ground. Ness's second PK Thunder variant in SSB4 shares some similarities with this version.

PK Thunder 2
PK Thunder 2, or "PK Rocket", is the term used for hitting Ness or Lucas with their own PK Thunder while it is still under their control. The Japanese developers dubbed this move PK Jibaku (PK). The word jibaku means 'self-destruct' or 'suicide bomb,' a fitting term for a tactic that turns Ness and Lucas into human missiles. This technique can be used by Ness and Lucas. Doing so will transform Ness or Lucas into a human projectile, which will move in different directions depending on what part of the body is hit. If the Ness or Lucas makes contact with an enemy, he will deal a good amount of damage and knockback. CPUs playing as either Ness or Lucas are also programmed to use this strategy, but they only use PK Thunder 2 vertically, even in situations where only recovering horizontally or diagonally would prevent death. PK Thunder 2 is also Ness and Lucas's main method of recovery, given that it launches them fairly far in a straight direction. While using the move, the user will fall much slower. When PK Thunder 2 is aimed downwards towards the ground, Ness or Lucas will enter a lying position, facing downwards. In Super Smash Bros. Ultimate, an arrow denotes the direction Ness or Lucas will move in upon initiating PK Thunder 2; Special Zoom also occurs if PK Thunder 2 successfully connects against an opponent.

While it is a strong recovery move, it is also very linear and predictable. As the move causes helplessness if it ends in mid-air, it is extremely susceptible to gimps as the projectile produced by PK Thunder can be destroyed, absorbed, reflected, pocketed, or blocked by the stage.

In Smash 4 and Ultimate, if Ness or Lucas hit a wall during PK Thunder 2, they can use the move again in midair, but only during the moment between hitting the wall and entering their helpless animations. They can only do this once; hitting a wall again with the second PK Thunder without touching the ground or grabbing the ledge will result in immediate helplessness.

Ness's version
Ness's version of PK Thunder 2 deals one strong blow. If used up close in Brawl and Smash 4, it can bring Ness to a short stop. If Ness' PK Thunder 2 hits an opponent, it does 25% damage with extremely high knockback, KOing opponents at 75% in Melee, 50% in Brawl, and 30% in Smash 4. The distance of PK Thunder 2 can be shortened by angling it into the environment. If Ness hits a wall while flying, he'll bounce off of it as his flight direction is changed.

Ness' PK Thunder curves in a larger arc than Lucas, so Lucas requires less room to use PK Thunder 2 than Ness. However, Ness' PK Thunder is faster.

Lucas's version
Lucas's version of the attack hits multiple times, compared to Ness's one strong blow. It is interesting to note that Lucas's PK Thunder 2 covers more ground than Ness's, so Lucas's is slightly more effective when recovering. If all of Lucas's hits connect when using PK Thunder 2, it will deal a massive 43% damage in Brawl, 35.5% in Smash 4 and 32.5% in Ultimate with high knockback, making it Lucas' most damage-dealing move, with the exception of PK Starstorm, which cannot be used in competitive play. However, it is very hard to get full damage, as PK Thunder 2 takes very long to start and as such, is easily dodgeable. For tactical uses, Lucas's PK Thunder 2 can be used to "Thunderglide". Thundergliding is when the player runs off a platform then immediately uses PK Thunder. The effect should come out to being the PK Thunder being much closer to Lucas than normal. Then, guide the thunder into Lucas and he should angle down towards the ground. If performed right, Lucas's direction will go from diagonal to horizontal as he glides along the ground. Otherwise, he'll crash into the ground like a normal poorly aimed thunder. Lucas will stop at the edge on his own, making this move safe to use on a stage like Battlefield. It should also be noted that on stages like or  if Lucas's PK Thunder 2 is aimed wrong, the user will bounce right off the corner of the stage, leaving him in a helpless animation away from the ledge.

Customization
Special Move customization was added in Super Smash Bros. 4. These are the variations:

Ness

 * 1) PK Thunder: Default.
 * 2) Lasting PK Thunder: Doesn't disappear upon hitting an enemy, making it better suited for recoveries. This variation is slower, but has better control, similar to Lucas's version, except using this custom to initiate PK Thunder 2 means it only does about 25% damage — the same damage as the regular variant — compared to Lucas's PK Thunder 2 which can do up to 43% damage (however, they deal the same knockback). It is also of a dark indigo color, similar to Ness's PK Thunder in Brawl.
 * 3) Rolling PK Thunder: Has more power, but the lightning ball doesn't move as fast. Using PK Thunder 2 with this custom will also severely decrease the distance Ness travels, but deals more damage (25% → 30%). However, due to reduced base knockback, the KO percent is overall similar. Compared to the regular PK Thunder, it is a mint green color.

Lucas
Like the other DLC characters, Lucas has no custom move variations.
 * 1) PK Thunder: Default.

Origin
PK Thunder (localized as PSI Thunder in ) has appeared in all three games, where psychic power is used to send lightning at the enemy. In Earthbound and Mother 3, the move functions by damaging a random opponent, with a probability of missing altogether. Higher level versions of the move will fire multiple lightning blasts, each with an independent, randomized target. However, in the Mother series, neither Ness nor Lucas learn the move; instead it is learned by some of their friends and party members, and  in EarthBound and  in Mother 3 respectively.

The move's description in EarthBound states that the user could miss the target and not cause any damage to the enemy. The difficulty of using PK Thunder in the Super Smash Bros. games could be a reference to how PK Thunder can sometimes miss enemies in EarthBound. The move's recovery properties are somewhat similar to Teleport α, where the party's speed is increased greatly, to the point of being difficult to control, and explode if they hit a solid object before covering sufficient ground to warp.

Trivia

 * PK Thunder and Mach Tornado are the only moves that still have special animations when a boss is defeated (sparkling for PK Thunder and spinning for Mach Tornado).
 * If a character uses certain movement-inducing special attacks right after being hit by 's PK Thunder, they will move a larger distance than usual. Notable cases include 's Whirling Fortress.
 * In Smash 64, this move can be used to initiate the game-crashing PK thunder freeze glitch.
 * In  Super Smash Bros. Melee, only a level 9 Ness CPU will regularly use PK Thunder to recover. Level 8 and below will rarely ever use PK Thunder to recover.
 * In Melee, if Ness uses PK Thunder and gets attacked while performing it (unless the attack does not cause flinching), he will be covered in electrical sparks. This has been dubbed the Electric Ness glitch.
 * In Brawl, higher level CPUs of Ness and Lucas will use PK Thunder 2 to attack during matches — this can happen sometimes even at the start of a match. CPUs of these levels will also seldom use PK Thunder other than for recovery and aforementioned action. However, this is somewhat rare (especially for a level 9 CPU), and they will only do this when at the correct distance from another fighter.
 * In Brawl, if PK Thunder is spammed when Ness or Lucas are directly on top of a orange or green spring within a custom stage, he can stall inside of the spring for short periods of time. After a short amount of time, however, he will bounce out of the spring as normal. This also works with PK Flash.