Here's the 18th Boss for Mario & Sonic Worlds in Danger: Bowser Jr. and Metal Sonic. This takes place during the extremely long in planning Episode 21 when Mario, Sonic, Luigi, and Tails head to the Death Egg to take down Bowser and Eggman once and for all. But, Bowser and Eggman have tricks up their sleeves, and Bowser Jr. and Metal Sonic are just one of them.
Music: Judgement Day - Newgrounds Audio Portal
Flying Mario: jmkrebs30
Sonic: The Sonic Advance Custom Project
Bowser Jr: BrawlFan1
Metal Sonic: Domenico