The SupaMerge is an object and a key part of the plot in Mario + Rabbids Kingdom Battle. It is a technological visor that has the capacity to fuse two objects into one.
The SupaMerge was created by Genius Girl and her robot assistant Beep-0 with the intent to solve an energy crisis, but had a problem with overheating. As the inventor left for a break, the Rabbids showed up in their Time Washing Machine and began wreaking havoc. One Rabbid found the device and used it to merge the Rabbids with several different objects in the room, creating Rabbid Peach and Rabbid Mario before accidentally hitting the Time Washing Machine, causing it to malfunction and transport both Beep-0 and the Rabbids to the Mushroom Kingdom.
Upon arrival, the SupaMerge fused itself with the Rabbid who was wearing it. Bowser Jr. eventually befriended the Rabbid, naming him Spawny, with the intent to use the SupaMerge to create an army to take over the Mushroom Kingdom.