Grand Unifying Guesses/Nintendo

In the same universe

 * The castle in Ocarina of Time has pictures of several Mario characters in the windows.
 * Link's Awakening features Goombas, Piranha Plants, Chain Chomps, Wart and a Croco-lookalike. (The Wind Fish is apparently in charge of Sub-Con)
 * Most houses in A Link to the Past have portraits of Mario on the walls.
 * Super Mario Galaxy has "Electrogoombas", which in actuality are almost indistinguishable from Octoroks. (pink octopuses that spit rocks at you)
 * Link was in the bed in Rose Town in Super Mario RPG.

Mario comes first

 * The cross-references in the Zelda series are much more prevalent and explicit than those in the Mario series.
 * We already know there are multiple Links; therefore the Link in SMRPG still fits.
 * The Zelda game with the most references to the Mario series that wasn't part of a dream is The Minish Cap (Lakitus and Bob-ombs, among other things), which several theorists believe to be the earliest game in the Zelda timeline.

Corollaries

 * Metroid, F-Zero, Star Fox, and Pikmin also take place in the same universe, thanks to references in Super Mario RPG and Mario Golf: Toadstool Tour.
 * As does Donkey Kong Country, as seen in DKC3. If you buy the shell from Bazaar, ask about the castle, and refuse to pay the price, Bazaar says, and I quote, "Are you sure? Some cheeky lad called Link was in last week and he asked about the castle too. He didn't have enough coins, but he seemed such a nice fellow that I agreed to accept 500 rupees instead". And by extension, the newest Punch Out takes place in this world, as well.
 * Since F-Zero and Star Fox seem to take place in the distant future, Hinopio is probably a Time Lord.
 * Additional evidence to place F-Zero and StarFox in the same universe: both the arwings and the F-Zero cars are powered by G-Diffusor Systems, and James McCloud appears in F-Zero - one effect of being trapped in the Black Hole was to turn him into a human.
 * Either that, or Fox is a half-fox, half-human hybrid. The human half, obviously, is his vocal cords.
 * And his knees.
 * Strange inconsistencies between Pikmin's Earth and our Earth are there because Pikmin actually takes place on the Mushroom World. Nintendo products there are not a problem, as they already exist from the Wario Ware games. Real-world brand name products were presumably brought there by the Mario Bros. when they went through the portal.
 * Alternately, the WarioWare universe is an alternate reality version of this universe, focusing on the exploits of their Wario. Alternately, if Wario Ware is set in the real world, Wario possesses the power to travel between our world and the Mushroom Kingdom, much like Mario and Luigi.
 * This also explains why Peach's crown was in Pikmin 2.
 * You want Grand Unified? Here's Grand Unified:
 * Kid Icarus takes place shortly after the stone age when Medusa used alchemy to turn people into stone. The Angel Pit didn't like it so he killed her.
 * A few tribes learned to read Medusa's alchemy books and used them to create their own world so they wouldn't have to share power. This explains why the world of Golden Sun looks like ours but is flat because it was created before anyone knew Earth was really round.
 * Maintaining the world was too hard, however, so everyone built rocket ships and colonized the solar system seen in Magical Vacation.
 * In the next Kid Icarus game, a demon named Orcos tries to unleash four ancient evils on us. He just barely got one through before Pit found and killed him and the other three ancients spend the rest of their lives trying to follow the first. Their story is told in Eternal Darkness.
 * Zelda takes place during the middle ages in a kingdom that is eventually lost.
 * At that point, the Oocca had left Earth and were evolving into the Chozo. The dragon Argorok's descendants continued to threaten them. Samus's foe Ridley is part of this lineage.
 * Fire Emblem takes place around the same time, on a different Continent
 * ... and one of the games takes place on Terminia.
 * When Mario and Luigi were born, they were brought through Mushroom Kingdom before heading to the 'real world'.
 * Donkey Kong Country occurs in the jungles of the real world
 * This has been disproven, as Bazaar, the shopkeeper in DKC3, has given Link information about the castle before you met him. See above.
 * The original DK headed to Manhattan and was stopped by Mario, who then takes a job as plumber.
 * After this, Mario falls back into the Mushroom Kingdom.
 * Wario, deciding to capitalize on everything, gets into the Game Industry in the real world (after being continually blocked from riches in the Mushroom Kingdom). He originally starts by selling the Mario story to Nintendo, but eventually forms Wario Ware.
 * The DK event resulted in people realizing that sentient animals exist. As a result, these animals started coming out of the woodwork, causing some people to live among them (Animal Crossing)
 * Wars break out, resulting in Advance Wars.
 * Advance Wars days of Ruin happens, resulting in a near-destruction of everything.
 * The animals escape the apocalypse by heading to the stars and forming the Lylat System.
 * Events of StarFox: Somehow James McCloud is turned human and disappears.
 * Further in the future, civilization gets back on track, and the F-Zero circuits are created, and the Metroid and F-Zero series occur.
 * Pokémon are created in a laboratory, and due to their hyper-abilities knock out most of the native creatures. After spreading to the Midwest of the United States, they impose a quarantine around the zone. Some technology remains (such as Poké Balls, based on reverse-engineering the Morph Ball), but otherwise the people forget about everything beyond the wall.
 * A parallel experiment lead to Geist.
 * Note: All games that reasonably could take place in the real world (such as Punch-Out!! and Wii Sports) do.
 * Super Smash Bros is set at the very end; only the main characters of all games remain, kept alive by Contractual Immortality.
 * The Kirby games are also linked; the Boos from the Mario series are the ghosts of the denizens of Kirby's world, mostly the Waddle Dees. King Boo, their self-proclaimed ruler, is the ghost of King Dedede.
 * Then where does the Earthbound series fit into all this?
 * Eagle Land is from the imaginations of the people of Pop Star, and Gigyas is the result of influences by Nightmare, Dark Matter, Zero, Zero-Two, Marx and Marx Soul.
 * After the defeat of Gigyas, things calm down and the first Custom Robo is created.
 * In Kirby's Dream Land 3, Samus and some Metroids show up.

== Princess Peach of Super Mario Bros was originally a Toad but was hit with the Midnight Bliss attack of Demitri Maximoff from Darkstalkers, which was interrupted before she could be drained and reverted, leaving her an attractive human-like girl permanently. ==
 * It was put forward in this comic.

Ganondorf is the true mastermind of every evil plot ever.

 * We all know that he loves to hijack plots, so why does it have to be limited to Zelda? He has at least some of the Triforce, so what's stopping him?
 * Plus the Sacred Realm appears to be an intangible dimension in itself, so it could either be Purgatory or a dimension that links to every alternate universe.