The angle of an attack is what direction it sends opponents when it connects, such as horizontally, vertically, or diagonally. Many attacks have multiple hitboxes that possess slightly (or even significantly) different angles, so opponents being hit by different parts of one attack can be sent in different directions. Angle is a basic property of all hitboxes that has a major effect on an attack's effectiveness as a whole.
The angle of a hitbox is defined as a number of degrees and can span any integer number, where 0 equals "away from the attacker", 90 equals "straight up", 180 equals "towards the attacker", and 270 equals "straight down"; negative angles such as -90 can also be used (and depending on the game can carry an additional meaning). The definition of "away" versus "towards" is based on where the attacker and the opponent are positioned, not the hitboxes and hurtboxes involved. In SSB and Melee, this results in some attacks being able to send opponents in unexpected directions; Fox's back air and Captain Falcon's Knee Smash in Melee are notable examples of cases where players intentionally try to land "reverse" hits for combo purposes. Starting in Brawl, it is possible for a hitbox to define whether this behaviour holds, or whether the opponent is always sent in a specific direction, which is used to eliminate many of these cases.
Generally, no one angle is better than any other; two otherwise identical attacks that have differing angles will often have different purposes. One of the most dramatic of these comparisons is in Melee: despite Fox's and Falco's Reflectors having very similar properties, and both being central to their characters, they have completely different usages in competitive play. A character that lacks a type of move within one of these broad classes (for example, a vertical KO move) will often be at a disadvantage compared to a character that has at least one of every option.
Certain angles are dynamic, changing the exact direction they launch based on additional factors.
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