Which studio co-developed Smash 4 with Sora Ltd.?

The studio that co-developed Smash 4 with Sora Ltd. was Bandai Namco Studios.

Super Smash Bros. for Nintendo 3DS and Super Smash Bros. for Wii U were developed jointly by Sora Ltd. and Bandai Namco Studios. Sora was the company associated with series creator and director Masahiro Sakurai, while Bandai Namco supplied staff and expertise from projects including Tekken and Soulcalibur. Nintendo published the games.

The collaboration was a major change from the earlier development history of the series. HAL Laboratory had assisted with previous Smash entries, especially the Nintendo 64 original, Melee, and Brawl, so HAL Laboratory is an understandable but incorrect choice for Smash 4. Retro Studios and Monolith Soft are also Nintendo-affiliated developers, but neither was the credited co-developer for this installment.

Smash 4 began development after Sakurai completed Kid Icarus: Uprising. The two versions were designed for Nintendo 3DS and Wii U, with shared rosters but some platform-specific stages and modes. The same Sora–Bandai Namco partnership later returned for Super Smash Bros. Ultimate.