The Great Collision is the story mode for Randamu Warriors.
It happened a while ago, at Final Destination. Some of Nintendo's greatest All-Stars, (plus Snake, because why not,) were ready to face Tabuu, leader of the Subspace Army. Hope seemed lost until one hero came and ultimately destroyed Tabuu. His name.....was Sonic the Hedgehog.
Tabuu's remains drift throught the cosmic links between the universes as a vortex. An outside force, one of the very few who can break through the boundries of the universes, decides to use this power for his own gain, to toy with some of the greatest heroes in the multiverse. He creates a world out of chunks of previous worlds, using the vortex's energy. After this new universe has been made, this force re-awakens the Subspace Army.
Doomsday is about to begin.
In present time, Sonic is fighting against Eggman's Badniks, as usual. After defeating a few, he discovers that the power source for the robots are shadow bugs. He runs off to tell Tails about his new discovery.
Ruins of Ponyville
Twilight Sparkle wakes up to find Ponyville completely destroyed, and the remnants of the city are infested with Primids. After defeating the Primids, Twilight comes across a shadow bug-infested Pinkie Pie. After defeating Subspace Pinkie, Twilight returns Pinkie Pie to her normal state and the two meet up with Sonic and Tails, who pile into the Tornado and escape.
The Mystery Shack
It's a normal day at The Mystery Shack until Dipper & Mabel find out that the clone machine is missing. They are unaware of the fusing of the worlds until they find out that Trixie is the one who stole the machine, and sends her clones after them. After defeating her clones, Dipper & Mabel face Trixie. After defeating Trixie, she decides to reluctantly help the heroes, telling them that a mysterious cycloptic creature forced her to help him. Dipper identifies this creature as Bill Cipher. Dipper, Mabel, and Trixie head into the golf cart and try to find out what's going on.