I am going to try and write it up in fairly generic terms, with an old school D&D slant
Shadows to lead
Casting Time: 1 round
Range: Max 500'
Duration: 3 Turns + 1/ 3 levels of the caster
Save: Spells or Will or whatever is applicable.
Components: The material component for this spell is lead shavings covered in black ink.
Description: When cast this spell makes the victims shadow the weight of a giant mass of lead weighing 600lbs + 50lbs per level of the caster. If the victim can actually carry/lift this type of weight the spell acts only as a slow spell. But if the vitim cannot bear the weight they are pulled down to the ground and held there under great duress. The victim must make a strength check (or equivalent) every turn or suffer 1d6 in crushing damage.