Super Mario doesn't believe in God.
For all his magical items, heroic deeds and self-sacrifice, Mario knows - simply knows - that there is no external, mystical force shaping events and willing to intervene on his behalf. There's the player, of course, but once he boots up the system and grabs the controller, the player and Mario are one and the same. Mario, and Mario alone, is the only person who can save the Princess, defeat Bowser and restore order to the land. No invisible, benevolent overlord. No God. And he likes it that way.
Antitheism, as defined by journalist and author Christopher Hitchens, is essentially the belief that it would be better to live in a godless universe than one ruled by "round the clock, divine supervision"; that not only is God likely nonexistent, but that our universe is all the better for his absence. Though this might not seem an unusual point of view coming from the Hitchens' or Dawkins' of the world, it is far more surprising to attach the same philosophy to, say, Mario and Luigi.
The vast majority of videogames, from Metal Gear Solid to Super Mario Bros., take place in atheistic universes. When Solid Snake duels against a Metal Gear armed with nothing but a stinger missile and a pocketful of rations, there is no (in this case, literal) deus ex machina waiting in the wings to destroy the walking robot should Snake get too close to death. Snake is the only person who can destroy the Metal Gear; there is no God watching the battle who will occasionally grant miracles in Snake's favor.
Describing this sort of gameplay as godless may seem obvious; in many ways, it's simply good game design. Every game gives the player some degree of control over their environment - the existence of a supreme being who supersedes all player commands would be frustrating to no end. If the player's actions can be overruled at the whim of another character, why should the player even play? Why not turn the game into an extended cut scene if player input is so unimportant?
Because of this, most games must take place in atheistic universes and thus are antitheistic by nature. It is clearly better to play a videogame taking place in a world without a god than a world with one.
Then again, one can't forget the so-called god simulators - games like Civilization, Black & White, or Spore that claim to put the player in the position of a supreme being, leaving him free to shape the universe to his will.