The way the announcer says Bowser Jr.'s name in Smash is like "Bowser Junior?" Combined with the announcement you get: "And the winner is... Bowser Junior?"
Smash Ultimate changes the victory message to accommodate teams and Ice Climbers, leaving us with "Bowser Junior? wins!"
This is all to say that "Bowser Junior?" lives rent free in my head, and surfaces any time anything has Jr. appended. (Most recently Splattershot Junior?)