Sleipnir has eight legs - it is said that it represents the 8 legs of a coffin (4 to stand on, 4 handles (legs) where the coffinbearers take it), or the 8 legs of the 4 coffinbearers themselves, representing that you can ride Sleipnir into the realm of death (which Hermodr did when trying to rescue his brother Baldr) or that Odin rides his own coffin into war, given that he is foredoomed to be killed by Fenris during Ragnarök.
Sleipnir has eight legs - it is said that it represents the 8 legs of a coffin (4 to stand on, 4 handles (legs) where the coffinbearers take it), or the 8 legs of the 4 coffinbearers themselves, representing that you can ride Sleipnir into the realm of death (which Hermodr did when trying to rescue his brother Baldr) or that Odin rides his own coffin into war, given that he is foredoomed to be killed by Fenris during Ragnarök.