A Geometry Dash portal has torn open beside the Ruined Chapel bench in Moss Grotto, the first bench in Silksong. Step in, and Hornet auto-runs Stereo Madness: the real level, its song, blocks, spikes, ship sections and sounds, read from your own Geometry Dash install while you play, with GD's own physics.
In the rift
One button, as in GD: Silksong's Jump jumps, and holding it flies the GD ship (painted in Hornet's colours).
Hornet runs and leaps with her own Silksong animations.
GD's progress bar, the attempt counter, the level's colour changes and its three secret coins.
Touch a spike and the attempt restarts. Your best % is saved for each save slot.
Finish the level to earn 100 rosaries the first time and 10 each time after.
Press Dash to leave whenever you like. Pausing the game pauses the rift and its song.
You need
Hollow Knight: Silksong. Melty installs BepInEx 5 for you.
Geometry Dash (Steam) installed on the same PC. Dash Rifts finds it on its own and reads the level, music and art from it. Nothing from either game is included. If Geometry Dash isn't found, the rift tells you so in the game. If it's in an unusual folder, set GeometryDashPath in BepInEx/config/melty.dashrifts.cfg.