Worlds Collide

Worlds Collide, also known by the much longer title Sonic & Mega Man: When Worlds Collide, is a 12-part crossover storyline between the franchises Mega Man and Sonic the Hedgehog announced on the San Diego Comic-Con International on July 10, 2012, published by Archie Comics' Mega Man, Sonic the Hedgehog and Sonic Universe comic books in 2013.

Story summary
After the first Genesis Wave, the blue Chaos Emerald from Sonic the Hedgehog's world had disappeared. Some time later it was found by Dr. Wily in Mega Man's world, and while analyzing it, Wily accidentally entered in contact with Dr. Eggman. Both villains decided to work together, creating the Skull Egg Zone to reunite and plot against their blue nemeses, first creating the Wily Egg, where they cause a new Genesis Wave to alter the reality of their worlds, and they are the only persons who retain the memories of both their original and new lives. The timeline of the altered realities from both Mega Man's and Sonic's worlds are apparently based on the video game series instead of the comics, being set after the events of recent video games like Mega Man 10 and Sonic Generations.

The doctors proceed to collect the other Chaos Emeralds for their main plan, and they capture Sonic's friends to turn them into Roboticized Masters and help in their search. While stealing a Chaos Emerald from Mega City, Mega Man confronts the Roboticized Masters and follows them, being lured to enter Sonic's world by a Warp Ring. There, the doctors trick Mega Man and Sonic to fight each other by using Copy Robot and Metal Sonic, but unexpectedly, Dr. Light manages to bring Mega Man back to his world, alongside Sonic. After learning of their mistake and rescuing Tails, they go to Light Labs, where they witness Bass and Metal Sonic entering a Warp Ring with Dr. Light. By analyzing Dr. Light's data, Tails manages to reopen the Warp Ring and the heroes enter the Skull Egg Zone.

Mega Man, Proto Man, Rush, Sonic, and Tails confront Copy Robot and the Genesis Unit, and later the Roboticized Masters, returning them to normal one by one. Meanwhile, inside the Wily Egg, Rouge the Bat trades information with Dr. Light, and she tries to sabotage the Wily Egg, but is captured and transformed in a Roboticized Master. She, alongside an army of revived Robot Masters, are sent after the reunited heroes, now including Sonic's restored friends and E-123 Omega. Eggman notices that Dr. Light could cause trouble to their plans even while being held prisoner, and decides to kill him by dropping him from the Wily Egg, which angers Wily and makes both doctors plan to backstab each other. Rouge is restored and Dr. Light is saved by Shadow the Hedgehog, and while everyone takes care of the army of Robot Masters outside, Mega Man, Rush, Sonic, and Tails invade the Wily Egg. After dealing with several menaces, including the Mega Man Killers (with Tails being injured and sent back to the others with Rush), Chaos Devil (which is fought by Duo), Metal Sonic, and Bass, Mega Man and Sonic are captured by the doctors, and they reveal their plan to create a Super Genesis Wave to completely change their worlds.

When the group outside gain support from Dr. Light's original eight Robot Masters, Dr. Light, Proto Man, Rush, and Knuckles enter the Wily Egg and rescue the blue heroes. Eggman and Wily try to stop them with the Egg-Wily Machine X, but as they sabotaged each other, they are unable to fight and make a truce to repair it. They start the Super Genesis Wave, apparently winning, but while Proto Man and Knuckles were facing the doctors, Sonic and Mega Man used the Chaos Emerald to perform a super transformation, easily defeating the Egg-Wily Machine X. Although the reality of their worlds were completely changed, Sonic teaches Mega Man how to revert them back to normal. Mega Man successfully restores his world, but Eggman, unwilling to accept defeat, interferes with Sonic's attempt to restore the reality from their world.

Mega Man

 * Mega Man and all those from his world retain no memory of the event as said world was restored to nearly as it was before. Mega Man himself, briefly recalled Worlds Collide only to forget it upon the Genesis Wave's effect being undone. After effects include:
 * Dr. Wily despite forgetting everything had an urge to stomp on a carton of eggs, due to left over feelings of betrayal from Dr. Eggman. Incidentally, his video logs had no recollection of Dr. Eggman or the Blue Chaos Emerald.
 * Proto Man regressed back into Break Man. His damages to Mega City, Mega Man, Bomb Man, Guts Man and Cut Man was undone.
 * Aside from the above, Short Circuits alluded to the arc by comically implying that Break Man's attack "broke" the story for four months.
 * Later, during the Dawn of X story arc, when Xander Payne was traveling forwards through time to the world of Mega Man X, he came across the part of the crossover when Mega Man and Sonic worked together to battle Tails Man, confirming that the events of the crossover are canon to the Mega Man timeline, and from Mega Man's perspective, he won't witness them until much, much later.

Sonic The Hedgehog

 * Sonic the Hedgehog, Dr. Eggman, and Blaze the Cat remember the event, with Tails remembering it not long after things were restored. Due to Eggman's interference with the restoration of the world, however, Sonic's world changed greatly in contrast with Mega Man's world. Several characters ended up in different locations. (Sonic the Hedgehog #252 & Sonic Universe #55) Examples include:
 * Sonic and Tails went from being in the Northern Tundra (where they were Pre-Genesis Wave) and were brought back to New Mobotropolis.
 * Dr. Eggman, along with Orbot and Cubot went from being in the Northern Tundra to the Efrika Plains. The remains of the Egg-Wily Machine X ended up there as well.


 * History in Sonic's world has also been altered. One example of such is the events of the video game Sonic Colors being canon, as well as that being the last time that Sonic and company saw Silver the Hedgehog.


 * The Wily Egg ended up in the Sol Zone. It was found by Captain Metal, who remodeled it into the Egg O' War. It was eventually powered by the Sol Emeralds, and would later contain a back up of Captain Metal's programming (revealed after Blaze destroyed his body). Using the Emeralds herself, Blaze became Burning Blaze and managed to defeated the Egg O' War which sunk to the bottom of the ocean, but is still online.

Trivia

 * Information revealed suggests that the crossover ultimately proved to be vital to the survival of both comics.
 * Around the time the crossover was beginning, Sonic writer Ken Penders had split ties with Archie and was suing for the rights to all the characters he created for the book, which would have severely compromised the ongoing plotlines had they been removed. The use of the crossover to reboot the comic was needed to both remove his works without further legal drama while allowing for a more game-related storyline with enough elements of the comic's previous state.
 * Around the time of the release of Worlds Unite, Archie writer Ian Flynn revealed that had the crossover not taken place, the Mega Man comic would most likely have been cancelled due to not meeting sales expectations.