For one reason or another, Nintendo had the Shovel Knight amiibo listed as compatible with Super Smash Brothers for 3DS and Wii U, suggesting Shovel Knight DLC is a very real possibility.
Yacht Club Games, the developer of Shovel Knight, however, has denied that Shovel Knight will be coming to Super Smash Brothers, tweeting “Appreciate the enthusiasm for the idea, but I believe this listing was made in error.” Though the last time Yacht Club Games was in this situation, after a retailer listed a physical copy of Shovel Knight, their denial ended up meaning very little.
Whether or not this definitively means Shovel Knight will become a playable character is still up for debate.