Oh, that's nice. I'll make this a thing.
3DS unlocks for DLC characters:
- Mewtwo: Clear Classic on 7.5 or higher as Pikachu or Charizard or play 130 vs. matches. Unlock match stage: Unova Pokémon League
- Lucas: Hit Sandbag over 300.0 meters/984 feet on Home-Run Contest as Ness or play 140 vs. matches. Unlock match stage: Magicant
- Roy: Clear Classic mode as Marth, Ike, Robin and Lucina on any difficulty or play 150 vs. matches. Unlock match stage: Arena Ferox
- Ryu: KO 1 opponent on Cruel Smash as Mega Man or play 160 vs. matches. Unlock match stage: Suzaku Castle (which would be unlocked alongside Ryu)
- Cloud: Clear All-Star mode as 20 characters or play 170 vs. matches. Unlock match stage: Midgar (which would be unlocked alongside Cloud)
- Corrin: Get a score of 20 on Rival Smash as Robin or play 180 vs. matches. Unlock match stage: Arena Ferox
- Bayonetta: Get 200 KOs on Endless Smash or play 190 vs. matches. Unlock match stage: Umbra Clock Tower (which would be unlocked alongside Bayonetta)
Unlock criteria for DLC stages:
- Dream Land (64): Clear Classic mode as Kirby on 7.0 or higher.
- Peach's Castle (64): Win 10 matches as Peach in versus mode.
- Hyrule Castle (64): Win Smash Run final battles as Link, Zelda, Sheik, Ganondorf and Toon Link.
- Super Mario Maker: Win 10 matches as Mario in versus mode.
- Duck Hunt: Clear Classic mode on any difficulty as Duck Hunt.
- Ryu, Cloud and Bayonetta's stages would be unlocked alongside their characters.
Would do Wii U as well, but I've spent enough time with this already.