According to Nintendo of America’s website, the Shovel Knight amiibo figure is compatible with Super Smash Bros. for Wii U and Nintendo 3DS.
Yacht Club Games’ Shovel Knight amiibo is listed as a “customizable amiibo figure for training in battle” for both versions (here and here) of Super Smash Bros. Keep in mind, however, that the information could be the result of human input error.
In addition, the Shovel Knight amiibo is listed as a compatible figure for the newly released Nintendo 3DS title Chibi-Robo!: Zip Lash. According to the Chibi-Robo amiibo webpage, players can use the Shovel Knight figure to “earn in-game coins.”
In late August, Nintendo and Yacht Club Games revealed the new figure during the pre-PAX Prime event held in Seattle’s EMP Museum. The developer is still working on a release date for the upcoming NFC toy.
Many fans suspect that Nintendo will announce Shovel Knight as a playable character in Super Smash Bros. given the character’s popularity among fans, and for the Smash Bros. Fighter Ballot.
On a separate note, someone found three empty character slots buried within the Super Smash Bros. game files earlier this month.