[[quoteright:180:http://static.tvtropes.org/pmwiki/pub/images/180_5645.jpg]]
''Mario and Sonic: Heroes Unite!'' is a {{Crossover}} FanFiction between the ''Franchise/SonicTheHedgehog'' and ''Franchise/SuperMarioBros'' franchises, created by [[http://www.fanfiction.net/u/2434291 Azurixx]]. It can be found [[http://www.fanfiction.net/s/6122988 here]].

The story starts as any Sonic game would go: Sonic's ArchEnemy Dr. Eggman attacks Empire City and Sonic goes to stop him. A fairly common task for Sonic.

That is, until a portal suddenly shows up and sucks Sonic, Tails, Amy and Eggman inside.

When Sonic goes back into his senses, he finds himself in the Mushroom Kingdom. Now he has to find a way to find the rest of his friends who also got sucked up return to his world. Unbeknown to him, though, an evil force, bigger than Eggman and Bowser's powers combined, is threatening both of their worlds...

The story's divided into three parts: "The Mario World Saga", which corresponds to chapters 1 through 46, "The Sonic World Saga", which corresponds to chapters 47 through 92 and the "Finale Saga", which corresponds to the remaining chapters.

As of August 27th, 2013, all 100 chapters have been posted and the story is completed!
----
!!This FanFic contains examples of the following tropes:
* ActionGirl: Amy is much more involved in battles in this story than she is in the current Sonic games.
* {{Adorkable}}: Yoshi is a beloved fan favorite because of this.
* AprilFoolsDay: According to the author's note from chapter 58, the author pulled out one of these when he pretended he was going to "leave" the story and stop writing. It ''was'' meant to be a harmless prank, but people reacted on the negative side.
* [[spoiler:AlasPoorVillain: Bowser ends up being killed protecting Peach from an attack from Malevo.]]
** [[spoiler:He got better thanks to some 1-ups at the end of chapter 97.]]
* AttackOfThe50FootWhatever: Eggman's [[spoiler:Doomsday Machine.]]
* BackToBackBadasses: Mario and Sonic
* {{Badass}}: Mario, Sonic, Knuckles, DK, and Shadow stand out
** BadassAdorable: Yoshi
** BadassBookworm: Tails
** BadassPrincess: Peach, Daisy, and Blaze
* BadassCrew: Mario's team and Sonic team working together and taking down enemies!
* BashBrothers: Mario and Luigi, for the crossover however it becomes Mario and Sonic
* BigBadDuumvirate: Bowser and Dr. Eggman.
* {{Big Damn Hero|es}}: After [[spoiler:Metal Sonic used Chaos Blast]] to severely injure Sonic, Tails and Amy, it seems like he has the upper hand... that is, until Mario shows up and throws Sonic the red Chaos Emerald.
* BigEater: Yoshi REALLY loves food.
* BiggerBad: Metal Sonic.
** [[spoiler:There's an even BIGGER Bad, a dragon by the name of Malevo, the ruler of the Negative Dimension that Metal spent a long time trying to get into, and now that there's a pathway between Sonic's World and Mario's World, he's gonna level both of them to show the worlds what negative energy can really do! Believe it or not, this guy, NOT METAL, is the guy described as "bigger than Eggman and Bowser's powers combined"]]
* BigWordShout: In chapter 82, as Bowser is delivering the smackdown to [[spoiler:Metal Sonic, Bowser Jr. suddenly yells for him to stop.]]
* BookEnds: Of a sort. Chapter 2 has Mario saving Sonic from drowning in the lake in Princess Peach's castle. The second-to-last chapter of the Mario World Saga has Mario and Sonic staring at that same lake.
* {{Cliffhanger}}: TheReveal is actually done at the end of chapter 38. That should tell you something.
** [[PlayingWithATrope Played with]] in chapter 43, see InterfaceSpoiler below.
* TheChosenOne: The Seven Star Children are the chosen ones to open the Negate Dimension with the 7 [[MacGuffin Chaos Emeralds and the Master Emerald.]] [[spoiler:Mario, Luigi, Princess Peach, Donkey Kong, Yoshi, Wario, and Bowser are the Star Children.]]
* {{Cloudcuckoolander}}: Yoshi is a more grounded version of this trope. Some of the stuff he says is weird, but he still has plot clarity.
* CommonCrossover: Sure, crossovers between Mario and Sonic have been done to ''death'' already, but Azurixx managed to create an actual ''original'' story based on the two franchises.
* ContinuityNod: Remember the ExcusePlot of ''YoshisIsland DS''? Well, that comes up a lot, because it's very important in the story.
** When Sonic is traveling through the underground cave in chapter 3, he claims that is darker than [[VideoGame/SonicTheHedgehog1 Labyrinth Zone]].
** [[VideoGame/PaperMario64 This isn't the first time]] [[VideoGame/PaperMarioStickerStar we've seen a replica of Bowser.]]
** Just before firing the missiles of the Giant Bowser Mecha, Eggman says "Sayonara, Sonic the Hedgehog!". A similar line was said by Sonic and Maria in ''VideoGame/SonicAdventure2''.
** Sonic talks to a turned off [[spoiler:Metal Sonic, who Tails has been trying to hack after they returned home,]] when Tails walks in and asks "Were you just talking to the robot who can't hear you...[[VideoGame/SonicColors again?]]"
** After using a Chaos Blast attack in chapter 49, Metal Sonic mentions that it's been a while since he copied Shadow's data, referring to the events of ''VideoGame/SonicHeroes''.
** [[spoiler:When Luigi is working with Metal Sonic in finding the Chaos Emeralds for him, his appearance is the same as [[VideoGame/SuperPaperMario Mr. L's]], he did this mostly just in case they encounter the heroes, smart move Metal.]]
** When Bowser sees Eggman's badnik army, it reminds him of [[VideoGame/SuperMarioGalaxy Megaleg]] and [[VideoGame/SuperMarioGalaxy2 Megahammer]].
* CowardlyLion: Guess who, just guess.
* CriminalAmnesiac: [[spoiler:Luigi]] suffers amnesia following the [[spoiler:transfer to Sonic's world]]. Metal Sonic takes the opportunity to claim that [[spoiler:Luigi]] is on his side and that the heroes are actually his enemies.
* CrouchingMoronHiddenBadass: Luigi especially [[spoiler: when he's working for Metal Sonic. He gives Mario and Sonic a rough time after his amnesiac face-heel turn.]]
* DefrostingIceQueen: Blaze has always been shy around strangers and her cold side comes back when she's introduced to the Mario characters, but she eventually warms up to SOME of them.
* DiscOneFinalBoss: Mario and Sonic have defeated their [[ArchEnemy Arch-Enemies]] in Bowser's castle--which was completely destroyed in the process. Sonic and his friends then successfully return to their world. The story's over now, right? '''''Nope.''''' Cue chapter 46 and the Sonic World Saga.
** Another Disc One Final Boss happens in chapter 92. The heroes have destroyed Eggtropia after a fierce battle. Unbeknownst to them, Metal Sonic has reactivated and has left Eggman unconscious. Cue the Finale Saga.
* DistressedDamsel: Bowser (of course) kidnaps Princess Peach in chapter 2. And again in chapter 40.
* DoomsdayDevice: Eggman builds a [[spoiler:robotic duplicate of Bowser, powered by a Chaos Emerald, which he codenames the Doomsday Machine and names the ''Giant Bowser Mecha''.]]
* DudleyDoRightStopsToHelp: Sure, he's busy finding out the whereabouts of Tails and Amy, but even Sonic couldn't resist helping out a friendly Koopa Troopa in need.
* ElementalPowers: Sonic characters when using [[spoiler:powers-ups from Mario's world]].
** AnIcePerson: [[spoiler:Amy when she uses the Ice Flower.]]
** PlayingWithFire: [[spoiler:Tails while using the Fire Flower.]]
** InvincibilityPowerUp: [[spoiler:Sonic when he uses the Rainbow Star.]]
* EarnYourHappyEnding: [[spoiler:Sonic and Mario manage to beat Malevo and save their worlds, but now the guardian of the realms has shattered the link between the two worlds, leaving a sort of bitter-sweet ending.]]
* EleventhHourSuperpower: As per standard in the Sonic franchise, Super Sonic makes an appearance in Chapter 98. However, [[spoiler:Mario also goes Super in the following chapter. As the author puts it, this gives a whole new meaning to the term "Super Mario Bros.".]]
* EvenEvilHasStandards: "Massive obliteration to all worlds? Even I'm not crazy to take that kind of risk!"
* EvilIsNotAToy: [[spoiler:Malevo plans to show both Sonic's World and Mario's World this, by taking over and conquering both worlds. Metal Sonic already learned this the hard way when he offered Malevo the Chaos Emeralds in exchange for his power, only to be torn apart.]]
* ExactWords: "Tails said I couldn't destroy the robots. He didn't say they couldn't destroy each other."
* FaceHeelTurn: [[spoiler: Luigi, but its only because of amnesia.]]
* FiveManBand: Of all characters who go adventuring for Chaos Emeralds in the first half.
** TheLeader: Mario and Sonic
** TheLancer: Luigi
** TheSmartGuy: Tails
** TheBigGuy: Yoshi
** TheChick: Amy
** TeamMom: Peach
** SixthRanger: Knuckles
* FindOutNextTime: A narration summarizing the main events of the chapter is added after the "ToBeContinued" happens and before the Author's Notes for the chapter are displayed. Later chapters finish this narration with "Tune in next time for the next chapter of Mario and Sonic: Heroes Unite!" or variations of this phrase.
* FissionMailed[=/=]InterfaceSpoiler: Chapter 43 seems to end on a downer: Mario and Sonic are trapped, Eggman pushes the BigRedButton on his Doomsday Machine, doing his trademark EvilLaugh... it seems like the chapter's going to end on a cliffhanger... but you haven't reached the end of the page yet! It certainly doesn't end like this!
** Sorta happened when [[spoiler:Luigi]] managed to steal the Red Chaos Emerald from our heroes.
* TheFriendNobodyLikes: Wario
* FutureBadass: Silver the Hedgehog.
* {{Gasshole}}: Wario
* {{Glomp}}: Amy occasionally gives these to Sonic
** Yoshi gives one to Tails after they're reunited in the second half of the story. Tails is receptive, unlike Sonic, even though his plane had just been crashed in front of him.
* GrandFinale: The Finale Saga, obviously.
* {{Hammerspace}}: Sort of explained by having Sonic put the Glow Block he gained in chapter 3 into his pocket... somehow.
* TheHeart: Mario and Sonic branch the crossover teams together.
* TheHero: Mario and Sonic
* HeterosexualLifePartners: Mario and Sonic, obviously.
** After that Yoshi and Tails have the second closest crossover friendship of any of the characters and spend most of their time together in the first half of the story.
* {{Homage}}: Chapter 36 is one to ''Film/KingKong''.
* HostageForMacGuffin: The villains have [[spoiler:Peach, Amy, Cream, Rouge and Shadow]] taken hostage and demand that the heroes give the Chaos Emeralds that they have in exchange for them.
* IDoNotOwn: "-I do not own any Mario or Sonic related characters. They are property of Nintendo and Sega-"
* IntergenerationalFriendship: We don't know exactly how far apart in age the Mario characters are from the Sonic characters, but we do know that Mario and friends are adults, and that Sonic and friends are teenagers.
* IsThisThingOn: "Attention. 1, 2, 3. Uhm...is this mic on?"
* ItMayHelpYouOnYourQuest: Before storming Bowser's Castle, Mario receives an [[VideoGame/MarioParty Item Bag]]. His comeback was from the last item in said Item Bag.
** Sonic receives a [[spoiler:Power Star just before going back to his world. That same Power Star is used to power the Star Fighter]] the heroes use as transportation.
* ItOnlyWorksOnce: [[spoiler:The characters from Sonic's world can only use ONE power-up from Mario's world. They can only use that one power-up after it's first use. A symbol of said power up will be marked on their right hand underneath their gloves. Tails gets the Fire Flower. Amy gets the Ice Flower. While Sonic gets the Rainbow Star.]]
* {{Jerkass}}: Wario and Waluigi
** Shadow manages to piss off Mario with his ruthless behavior.
* JerkWithAHeartOfGold: Knuckles can be rude and abrasive, especially to the crossover companions, but he always helps his friends when they're in danger.
** Sonic has always been known for being snarky and his rude side sometimes surfaces when Amy annoys him.
* LastEpisodeNewCharacter: Knuckles appears later on in the first half of the story.
* LoadsAndLoadsOfCharacters: During the second half of the story all of the major Sonic and Mario characters come together to defeat their enemies.
* NiceGuy: Yoshi is the biggest one. Mario, Luigi, and Tails also count.
* NoHoldsBarredBeatdown: Bowser, filled with anger about losing his castle and never seeing his son again, completely trashes [[spoiler:Metal Sonic]] in chapter 82.
* OddFriendship: Given how different Mario and Sonic are in terms of personalities you would think they wouldn't get along at first. Mario is a more serious, grounded and to-the-point boy-scout hero, while Sonic is a snarky, taunting, risky, impulsive hero. However they get along just fine from the star.
** Yoshi and Tails. Yoshi is an incredibly bubbly and kind dinosaur who possesses a simple, enthusiastic, and borderline {{Cloudcuckoolander}} mind. Tails is much more reserved and serious while still being kind and he possesses a genius level intelligence. These two meet up when Tails first wakes up in Mario's world and become best crossover friends.
* PapaWolf: Look above.
* PluckyGirl: Amy Rose, oh so much!
* TheReveal: Chapter 39 reveals that the shadow figure who was responsible for bringing Sonic to Mario's world in the first place was none other than [[spoiler:Metal Sonic]].
** During Chapter 65 there's this:
--> '''Mario''': Mamamia...[[spoiler:Luigi]], is that you?
* RecurringElement: When ever a character gets some type of power-up, after a description it will say "[name of character] was now [name of form.]"
* RobotMe[=/=]UnwillingRoboticisation: The shadow figure turns Luigi into a robotic version of himself in chapter 32.
* RuleOfThree: Sonic, Tails and Amy are the only ''Sonic'' characters to get [[spoiler:power-ups from Mario's world.]]
* ScheduleSlip: Chapter 83 was released ''four months'' after the previous chapter. The following chapter was added in ''January'', and the chapter after that one was posted in July.
* ShipTease: Sonic and Amy in the first half, however, this subplot gets almost completely dropped in the second half.
** Knuckles gets a brief one with Rouge the Bat.
* ShoutOut: In the last chapter, [[spoiler:the being who controls all worlds and dimensional borders shows Sonic and Mario glimpses of other world, (from the same companies who make their games) which are respectively ''{{Franchise/Pokemon}}'', ''Franchise/TheLegendOfZelda'', ''VideoGame/JetSetRadio'' and ''VideoGame/SuperMonkeyBall'']]
* TheStoic: Blaze the Cat, sort of. She strives to be this, but much like her game counterpart, she has a bit of a temper problem.
* SuddenlyVoiced: Yoshi, Donkey Kong and Diddy Kong.
* SurroundedByIdiots: Knuckles, of all the characters, gets one when he ends up paired with Donkey Kong and Wario for a mission.
* TakingYouWithMe: "If my castle is going down, I'm taking that plumber with it!"
* ThisIsGonnaSuck: "This...looks...baaaaad."
* TokenEvilTeammate: Even before [[spoiler: Bowser and Eggman switch sides to defeat the biggest bad from the negative dimension]] Mario and Sonic had a more toned down version of this character, and that character is [[spoiler: Wario]].
* TookALevelInBadass: Amy Rose is much more capable than she is in the games.
* TookALevelInJerkass: Shadow. In the games he's mostly just cold and pragmatic. Here, he's also abrasive.
* TookALevelInKindness: Silver the Hedgehog is much nicer in this fic than in other forms of media.
** Also applies to Amy Rose who is much less temperamental in this story.
** Donkey Kong isn't as mischievous as he is in other incarnations.
* VillainousFriendship: Bowser and Eggman team up
** [[spoiler: Bowser Junior and Metal Sonic form an alliance]].
* VillainousRescue: Metal Sonic saves Mario and Sonic from the Giant Bowser Mecha's missile attack in chapter 43 -- simply because Mario is necessary for his plan, nothing more.
* VitriolicBestBuds: Bowser and Doctor Eggman team up to defeat their arch enemies, but end up getting on each other's nerves all the time.
** Knuckles invokes this with Sonic and the crossover characters he interacts with the most, mainly Luigi and Yoshi
* WantonCrueltyToTheCommonComma: Minor, and only happens mostly on the first few chapters.
* WillTheyOrWontThey: While Sonic and Amy are in Mario's world, hints that there might actually ''be'' a romantic interest between the two of them are seen. When they return home it appears to be gone, but they have a touching moment when the first fly in the Star Fighter during Chapter 64.
* WordOfGod: This is part of the reason [[spoiler:Sonic's [[OnlyWorksOnce ONE]] power-up is the Rainbow Star. Its effect is similar to [[VideoGame/Sonic3AndKnuckles Hyper Sonic]].]]
** As of Chapter 88 (07/16/13), Azurixx said the next few chapters (89-92) will be posted with great speed.
* YouHaveGotToBeKiddingMe: Several characters pronounce this phrase every now and then, like Knuckles when he finds out Donkey Kong beat him at a game of blackjack.