After being announced on relatively short notice, the March 8th, 2018 Nintendo Direct ended with an unexpected announcement.
The teaser starts with a short scene of a shootout between two inklings amidst a white void. As they're fighting, their surroundings go dark, and the inkling girl turns to see a bright, glowing object behind her. As the reflection in her eye comes into focus, we catch a glimpse of the object - a burning Smash Ball emblem.
After zooming out to see how enormous it truly is, we catch a glimpse of two more characters: Mario and Link, both of whom are rendered in silhouette, illuminated from behind by the flames. Notably, Link seems to be wearing the Champion equipment from Breath of the Wild, rather than the traditional Hero's Tunic.
After a fade to white, two bits of text are shown on the screen: a Super Smash Bros. logo, followed by the year 2018. The message is clear: a new Smash game will be released by the end of the year. It is currently unknown whether it'll be a new game entirely or a deluxe release of Super Smash Bros. for 3DS and Wii U.
Smashboards will continue to provide coverage for this game as new information emerges.