Marth (SSBM)/Neutral special
Despite being a little sluggish compared to Marth's other moves, Shield Breaker is a surprisingly versatile move and fills many niches that the rest of Marth's moves can't. As the name suggests, the move deals a very high amount of shield damage, breaking more than half a shield when uncharged and breaking a full shield when fully charged. The move deals 28% damage at full charge with average base knockback and very high knockback scaling, meaning it can KO well below 70%. Fittingly, the move is meant to break a shield then punish the resulting shield break with a KO. Similarly, this move is Marth's best punish for a whiffed Rest.
Shield Breaker's primary use is being Marth's best move to cover high recovery options. While Marth's forward smash is a little faster and is used in similar situations, Shield Breaker has much better hitbox duration and slightly more reach, hitting higher, farther back and even hitting below the stage lower. Shield Breaker also has the benefit of a longer charging period meaning it can cover many more options than forward smash could. For example charging Shield Breaker will cover both an up special and shortened side special from Fox or Falco at the same time, whereas using a forward smash requires a hard read on one or the other. Another notable example is that Shield Breaker can cover all regular angles and fade backs from Captain Falcon's or Ganondorf's up special, whereas again forward smashing requires different timings. Another advantage Shield Breaker has over forward smash is that it doesn't extend Marth's hurtbox as much and better shields those hurtboxes with its hitboxes. Marth's forward smash on the other hand, extends the hurtbox of his arm and head before producing a hitbox, and also because the forward smash's animation has less hitbox duration and makes Marth lean forward more, the lower half of Marth's body (particularly the knee) is still very vulnerable to recovering opponents.
With some ingenuity, Shield Breaker can also use to platform tech chase, sometimes to better effect than Marth's up tilt, forward smash, or up air, as all three of these options can be shielded. While Marth can waveland on to a platform and grab the opponent, a faster and better option would be to jump slightly below the platform and use Shield Breaker. If the opponent continues to shield, the move will likely break the shield. The move's reach also allows it to still hit if the opponent jumps out of shield and depending on the length of the platform, may or may not cover rolls or wavedashes out of shield. The move also covers opponents attempting to shield drop. Shield Breaker also has much more reach than any of Marth's aerials, meaning it is just as, if not more useful, as a finish to an aerial combo or an offstage edgeguard. A common example of this is when a forward air or a neutral air sends an opponent too high or far to be hit with another aerial in a Ken Combo setup. This blindspot is precisely where Shield Breaker hits.
Despite its massive utility though, Shield Breaker's below-average speed is its main drawback and is what keeps it relatively situational compared to the other moves. However with with good timing and clever play, the move is potentially Marth's most rewarding move onstage and is something all opponents must watch out for when fighting Marth.
* Releasing the charge between the final frame of a loop and the starting frame of the next counts as completing that loop. As a result, there is only a one-frame window to release a charge made of four loops, due to the attack automatically reaching and using full charge afterwards - though unlike similar moves, there is no practical advantage to doing do, as the "just under fully charged" attack does 1 less damage and equal knockback compared to the fully charged attack.
Resulting charge levels