Working as a chargeable move that cannot be stored, Straight Lunge involves Little Mac stepping back to charge up a powerful, forward-sliding straight punch. It differs from other chargeable moves (apart from Ultimate Uppercut) due to its unique property of not gaining damage unless fully charged; the level of charge only increases the distance Little Mac lunges, while damage remains the same.
During the entire charging period (and during a fully charged punch), Mac gains slight knockback resistance which can shrug off attacks that deal 8% damage or less. The charging process can only be canceled by letting the move fully charge or by pressing the special button again; however, Mac cannot unleash the attack until around a second has passed. All variations of the move hit the hardest in the first few frames, although the charged version loses comparatively less power than an uncharged lunge.
The move has two charge variations:
In stark contrast to its power in standard matches, a fully charged Straight Lunge has low knockback scaling, making it inferior as a finisher in Home-Run Contest when compared to the Home Run Bat since it doesn't send the Sandbag considerably further when it is at high percentages.
Like most of Little Mac's special moves, Straight Lunge has a unique 8-bit sound if he is using a Wireframe alternate costume. If Kirby copies him while in that costume, he uses the 8-bit sound along with his own voice.
Unlike most special moves when done as quickly as possible after jumping from the ground, Little Mac remains grounded when performing Straight Lunge this way. This makes it especially useful when repositioning him to properly land the attack.
When Little Mac's Power Meter is full, his Straight Lunge is replaced with a single-use uppercut named the KO Uppercut. While it has the word "KO" in its name, it is not a true one-hit KO. Regardless, it is one of the strongest standard special moves in the game, surpassed only by Ganondorf's Reverse Warlock Punch, a fully charged Flare Blade, and a Judge 9.
Getting a KO Uppercut requires Little Mac to either receive 100% damage or deal 333% damage to opponents (or, more likely, a combination of both) to fill up his Power Meter via his own attacks or melee-based items; thrown items do not contribute to the meter. Unlike other special moves, Little Mac can only safely hold a KO Uppercut for four seconds before it is vulnerable to being removed by any attack that causes Little Mac to tumble.
The attack itself can be considered similar to a fully-charged Wario Waft: it is immensely powerful yet extremely fast, hitting on frame 9 and dealing enough knockback to KO the entire cast at 35% (with the exception of Shulk in the Shield Monado Art). This is dependent on the opponent's weight due to the uppercut's strong vertical angle (Jigglypuff in particular only needing 12% to be at KO percentage). However, Little Mac's KO Uppercut suffers from high ending lag, making it very risky to attempt in a predictable manner should the attack miss. Fortunately, the move's quick startup and Little Mac's excellent grounded combo potential allows a KO Uppercut to true combo from many of Mac's moves, which will be explained in further detail below.
The attack itself has several properties to note:
Consistent with Little Mac's depiction as a very strong fighter on the ground and very weak in the air, the aerial version of KO Uppercut is drastically weaker, with no KO potential until 151%, and also becomes blockable. However, using the KO Uppercut while having any sort of forward momentum gives Little Mac some decent horizontal distance, which can help him get back onstage. This tactic can boost Little Mac's abysmal recovery on certain stages, notably ones with walls that allow him to wall jump, although it is a very risky tactic in general, since the move's high ending lag makes it extremely likely that he'll be KO'd anyway.
In Super Smash Bros. Ultimate, Little Mac will jump slightly when using the KO Uppercut before instantly returning to the ground, as opposed to the previous game where he remained grounded. This makes it more closely resemble the Star Punch from the NES Punch-Out!!. Alongside its faster speed, it is now easier to land and has a larger hitbox due to Mac's movement. The aerial version now grants good horizontal distance and can be used for an actual recovery due to its ending lag being reduced, but it is no longer unblockable.
Kirby can use the Straight Lunge via copying Little Mac, but does not gain a Power Meter and thus can only use the standard version of the move.
Due to the KO Uppercut's sheer ability to turn a game around, the move can be easily telegraphed despite its quick startup. However, Little Mac grounded combo prowess grants him a few combos he can use to give himself a better guarantee to land an Uppercut, giving him potentially one of the most potent combos-to-KOs in the game along with more mixups to play mindgames with the opponent.
Special Move customization was added in Super Smash Bros. 4. These are the variations:
*All custom variants of Straight Lunge do not alter KO Uppercut in any way.
The uppercut is a reference to Little Mac's signature move in the Punch-Out!! series, the Star Uppercut. This move deals considerable damage and has a higher chance of leaving Mac's opponents down for the full ten-count.
The power meter originates from the 1984 arcade Punch-Out!! If Little Mac keeps attacking the opponent, the power meter will fill, but taking damage will cause the meter to fall, unlike in Smash Bros. When the power meter is fully charged (indicated by a glowing "KO" similar to the meter in Super Smash Bros.), the player can perform one of two knockout punches, an uppercut or a body-blow, by pressing a button on the arcade cabinet depending on the position of the gloves. The only Punch-Out!! game to retain this system outside of the arcades was Super Punch-Out!! on SNES.