Mischievous Darkness is the story mode for Age of Fury.
Episode 1: Collision Chaos
In the Spursverse, Mephiles the Dark sneaks into Peach's Castle and kidnaps Spursverse Princess Peach. In-universe Mario chases him into an underground cavern, where Mephiles battles him. Before Mario can deal the final blow, however, Mephiles escapes through a mysterious portal with Peach.
Meanwhile, in the Eterniverse, Loki is up to his old tricks again, attempting to take over New York City. Iron Man is sent by S.H.I.E.L.D. to stop him, but Loki escapes through a portal similar to the one that Mephiles escaped through.
Now, Spursverse Mephiles and Eterniverse Loki meet in the Flow of Reality. Mephiles and Loki agree on a plan to steal the Master Emerald and harness its energy to take control of the meta-universe. But what they don't realize is that their respective universes are already being forced into one...