Chains of Tharizdun

You choose a creature within range as you cause fiery chains to erupt from the ground, attempting to bind the target. The target must succeed on a Strength saving throw or become grappled for the duration. On a failed save, the target takes 3d4 Fire damage at the start of their turn. The damage of the spell increases a dice level for each turn the target spends in the chains (to a maximum of 3d12). 

To escape the chains, a creature can make a Strength saving throw at the end of their turn to escape, ending the spell.