The Merging Effect

The Merging Effect is hypothetical virus that's been happening in the Mario/Rabbids universe. It started in the beginning of first game, then it affected the Mario universe, all Rabbid hybrids of different objects and living things, respectively. In the trailer of Sparks of Hope, it shows that it not only affected the Mario universe, it's been affected beyond the Multiverse which is why the Mario/Rabbid crew are in space.

The Merging Effect is only theorized, it is not yet proven by Ubisoft or anyone associated with it.