Threads of Acheron

You conjure a matrix of intertwining strands of light that bind to things like magnetism. The threads fills a 30-foot cube from that point for the duration. The threads are difficult terrain and lightly obscure their area.
If the threads aren’t anchored between two solid masses (such as walls or trees) or layered across a floor, wall, or ceiling, the threads create supports of braided threads that form acceptable alternatives.
Each creature that starts its turn in the threads or that enters them during its turn must make a Dexterity saving throw. On a failed save, the creature is restrained as long as it remains in the web it can use its action to make a Strength check against your spell save DC. If it succeeds, it is no longer restrained. 
The webs are susceptible to the Darkness spell. Any 5-foot cube of threads exposed to magical darkness or necrotic damage burns away in 1 round, dealing 2d4 necrotic damage to any creature that starts its turn in the threads.