Data miners never seem to take a day off — thanks to the relentless work of a Super Mario Maker data miner, we now know that the newest costume (#112) will be Sky Pop. For those that may not recognize the name, Sky Pop is a throwback to the original Game Boy’s Mario Land. So yeah, an incredibly obscure reference.
As detailed in a reddit thread, the Sky Pop operates as a normal costume with a Game Boy color-scheme and a distinct bunch of sound effects. If you have Mario Maker, you can try it out in the data miner’s level: 4078-0000-0121-4C73. Or, if you would rather just watch it in action, check out GameXplain’s video below: