Sleipnir

In Norse Mythology (also canon in Marvel) Odin hired a man to build a wall for him, the man asked for no payment of gold but in exchange he wanted to marry Odin's daughter Freya, the goddess of fertility and love. However Freya did not want to marry this man, so Odin gave the man an impossible task; He must build the wall alone, and he must be finished in six months. Should he succeed (which he won't) he'd earn the right to marry Freya, and should he fail Odin would just hire Dwarves to finish the wall for him. The Man accepted the challenge but made only one request, that he's allowed to use his horse to help him. Over hearing this Loki says "Why not, it's just a horse," so Odin lets him use his horse. The next day they spot the man building the wall and a mighty horse that can move more stones than 100 men! At the rate the two of them are working they would finish on time, so they blame Loki for convincing them to allow the man his horse, and send him to go distract it. After a few failed attempts Loki then decides to lure the Horse away by shape shifting into a beautiful white mare. As a Mare Loki runs off while the eager stallion follows him, but eventually the stallion catches up to Loki and they do some distracting in a funky way...and Loki ends up getting pregnant and gives birth to an eight-legged foal and names it Sleipnir!