Warning! The following contains SPOILERS for the novel American Gods and the American Gods season 3 finale.
The final episode of American Gods season 3 dropped a major clue towards the real identity of Mr. World. While the series has been dropping hints since the beginning that the mysterious leader of the New Gods was hiding something from even his most devout followers, it became even more brazen in teasing his treacherous nature over the course of season 3.
Reportedly the spirit of globalization, Mr. World typically manifested as a slender man in a business suit (Crispin Glover). While he was generally content to try and recruit the Old Gods to his side, Mr. World seemed to harbor a special hatred for Mr. Wednesday, an incarnation of Odin. American Gods season 3 found Mr. World manipulating events so that he could convince Laura Moon (who had her own grudge against Wednesday) to act as his assassin, while still offering himself and the rest of the New Gods plausible deniability as to being involved.
Over the course of American Gods Season 3, as he continued developing an organization app called Shard that would increase the power of the New Gods, Mr. World began to manifest in new forms. At one point he took on the appearance of an stunningly beautiful Tobagonian-American woman (Dominique Jackson). Later, he appeared as a strong Hispanic man (Danny Trejo) while he was engaging in some tough negotiations. While this shapeshifting hinted at how powerful Mr. World was, it was also a subtle clue as to his true nature. Yet this was nothing compared to the hints Mr. World teased as he captured the New God Technical Boy, intending to use him as a living battery to power Shard.
Mr. World revealed that Technical Boy, rather than being the New god of technology, was actually a bridge between the Old Gods and New Gods; the embodiment of human innovation, without whom progress was impossible. After capturing Technical Boy, Mr. World would then go on to say some particularly telling lines; "People say this is the age of technology. They're wrong. This is the age of manipulation." He then added, as Technical Boy demanded to know who he was, "Trickery is what I do best," before leaving the room whistling a happy tune.
These lines strongly suggest Mr. World is Loki, the Norse god of trickery and mischief. Renowned for his ability to change forms as it suits him, Loki is a complex figure in the classic myths. While he often causes trouble among the other gods, he is also usually the one who comes up with cunning plans that solve the problems he doesn't create himself. This aspect of his character is often lost in most modern stories based on Norse mythology (such as in Marvel Comics) with Loki being portrayed as an overtly villainous or demonic being.
The revelation that Mr. World is Loki will not prove a surprise to fans of the American Gods novel, as this point was a key part of the novel's story. With this hint having been dropped in the show, it seems likely that, despite having gone far afield at times regarding the plot of the original book, the American Gods series is moving towards the Götterdämmerung promised since its first season. The big question now is if Mr. World really has thought of everything or if someone else might have a trick of their own to play in American Gods season 4.