This is a topic for making the storyline.
SUDK and I are allowed to edit the post to change it but you can suggest something, I'll re-write it if necessary and I'll put it in this post.
The story starts with Mario, Luigi and peach running as fast as they can through some levels. A flashback appears over Mario's head showing Bowser stealing the final grand star, the greatest source of power in the Mushroom Kingdom. Mario starts fuming and runs faster. Luigi and Peach struggle to keep up.
*They go through a level in the Mushroom Kingdom.*
They run through a forest following the winding trail, when they turn a corner, they smash into something green. The green thing turns out to be link and they explain in a speech bubble how Mario's greatest source of power was stolen and so was link's, the triforce. Link's triforce was stolen by ganon and link and Zelda thought he saw him coming this way. So Zelda and Link team up with mario's gang.
*They go through another level and generally the same thing happens. You get to pick the characters you want to be.*
They bump into a cloaked figure who turns out to be ichigo. They meet up with ichigo, renji, toshiro, goku, vegeta and gohan. The dragon ball characters came because the dragon balls were stolen by Buu and the bleach characters came because the hougyoku was stolen by sosuke aizen.
*They go through another level and you can pick who you want to be again.*
Sonic and Shadow dash by them and stop to talk to them. Tails, knuckles and amy come up behind them. Sonic explains that the master emerald was stolen and knuckles starts fuming. (It's his job to guard the master emerald.) So they team up and they start walking. A few seconds pass and a stretchy hand goes in front of them. Luffy and his crew, Nami, Zoro, Usopp and Sanji come behind him. The one piece was stolen by buggy and alvida and they join the crew to get it back.
*They go to a water based level. You can pick out of the huge variety of characters.*
Eventually, they all get to a huge castle. It has the names of all the antagonists on the sign. They know it's the right place so they enter the castle.
*They go through a bowser's castle like place. You can pick any of the characters.*
(More will be added soon.)