I've been adding tons of undocumented games to IGDB, which is naturally mostly promotional flash games, and something I found out is that IGDB doesn't have pages for the non-character Smash DLC aside from a very small selection of Ultimate's Mii Costumes, so I've added the 3DS/Wii U stage DLC, and it'll be very funny when they show up on my Backloggd list alongside "Which One of SpongeBob's Front Teeth Are You?" and "Scrat's Cheestrings Meltdown".
...and Knuckles.