On April 17, as part of the Super Smash Bros. Ultimate version 3.0 update, the leaked Stage Builder mode and a new Video Editor mode will officially appear. A new Shared Content area will also appear to… share those stages and videos.
In Stage Builder, you will be able to create levels, using the touchscreen to make land masses or drop moving or spinning platforms. There will additionally be new elements to play with, like curtains that drop and obscure the stage. You can also just add decorative elements to stages if you want.
In Video Editor, you can import the videos you have saved to your Nintendo Switch and splice them together in a timeline. So basically, you can create your own highlight reels (or blooper reels!) now.
Whether stages or videos, you can share that new Super Smash Bros. Ultimate content via a new Shared Content area.
All of these details are in addition to Joker and Mementos, which also release on April 17.