The Grasping Dark

This necrotic attack draws the target into a jet black dimension. This realm is dark and full of the spirits of past victims and it manifests itself within the victim's own form. No matter what angle one views the victim from, he or she appears to be a flat silhouette. Within the silhouette, the viewer sees the victim receding into the distance, pulled by obsidian black hands. The silhouette then vanishes, and the victim is lost forever.

The target must succeed a DC 12 Constitution Saving Throw or begins to be pulled into darkness and becomes petrified for the duration. Based off the Saving Throw, the target has time to save themselves from this terrible death. The further the roll from succeeding the save, the faster the spell takes hold. During this time, if  a restoration spell is cast on the victim or they receive healing equivalent to their hit-point maximum, the victim is spared with no side effects. On a successful save the target takes 3d8 necrotic damage and has disadvantage on all ability checks for one round. Casting the spell at a higher spell slot increases the necrotic damage by 1d8 per spell slot above 4 and the Saving Throw DC. 

When this spell is cast at higher levels its Spell Save DC increases by 2 and the chart for its adds 2 "instantaneous" tiers where the target immediately is pulled into darkness.

Example as a 5th level spell: