My personal favorite incarnation of Vishnu was born as Narasimha the Man-lion. It’s pretty much exactly what it sounds like, he was born half-man and half-lion at the end of the Satya Yuga. This was the last of Vishnu’s incarnations to be born during this age of man. Narasimha defies the laws of nature and seeks to overpower mortals who attempt to find immortality in unnatural ways.
He specifically came into being when a mighty evil Demon became upset with his son praying to Vishnu and tried to hurt him. The Demon had received a boon (a wish) that he could not be killed by man or animal, inside or out, day or night, on earth or the stars, with a weapon either living or inanimate. So Vishnu manifested as Narasimha. With the body of a man, and the head and claws of a lion, he and killed the deomon using his claws under a courtyard threshold of his home at exactly dusk, while he lays on his lap. Therefore finding a loophole in the boon allowing him to protect the young boy.