Spacie, sometimes unabbreviated as space animal, is a collective slang term that refers to the following characters:
The term originated in the competitive Melee community, where players noticed that Fox and Falco not only have an extremely similar moveset, being clones, but also very similar physical attributes, such as high falling speed and gravity, and light weight. These similarities not only grant the two characters a similar playstyle, but also make them uniquely susceptible to similar counterplay, such as Marth up throw chain throw in Melee and Pikachu down throw chain throw in Brawl, as well as specialized combos like Jigglypuff's up throw Rest. Subsequent titles differentiated Fox and Falco more, by giving them different moves and slightly altering their attributes; however, their moveset and physical attributes remain very similar across the series, and as such the term "spacie" continues to see wide usage. Super Smash Bros. Brawl introduced Wolf, another Star Fox character with a moveset based on Fox. Although their movesets are only superficially similar and he is an heavyweight in Brawl and a middleweight in Ultimate, as opposed to a lightweight, the overall similarities to Fox and Falco still cause Wolf to be included among the spacies.
Similar to how they all share similar strengths, they also share very similar weaknesses: most of the spacies have poor survivability due to their low weight as well as being very vulnerable to combos due to their high falling speed (Fox having the lowest weight out of the three starting from "Melee" onwards and having the highest gravity in every game, though he didn't have the highest falling speed until "Smash 4" in the Smash series). They also have linear recoveries: their horizontal options all travel in a linear fashion, and Fire Fox and Fire Bird have a very high amount of startup lag, causing them to be vulnerable to opponent's edgeguarding options. Fire Wolf has less startup in comparison, but in Ultimate travels the shortest distance out of the three while Fire Fox travels the farthest distance.