Thorns of Darkness

Once this spell is casted it creates 20ft area from central point in each direction (square). Whenever anyone enters this area which is only highleded to you, must make a dexterity saving throw to avoid a dark thorn which eruptes from the ground dealing  d8 piercing damage on a failed save and half on a succeesful one. When they fail they are under the effects of grapple until they succeed on a str save of your stat. You can get yourself in this as well, however you are immune to the damage this would deal to you.