Acidic Swamp
A 30-foot diameter of ground sinks into caustic bog, thorned roots and steaming water. Each creature in the area makes a Constitution saving throw against your spell save DC. On a failure it takes (H + half your level)d4 acid damage and is Poisoned. On a success it takes half damage and is not Poisoned. A creature Poisoned this way repeats the saving throw at the end of each of its turns, ending the condition on a success.
Poisoned: the creature has disadvantage on attack rolls and ability checks.
A creature that fails the initial saving throw is also Restrained by the roots. It repeats the Constitution saving throw at the end of each of its turns, ending both conditions on a success. The ground stays difficult terrain for 10 minutes.
Acidic bubbles rise through the bog. As a lair action at initiative 20, choose a point anywhere inside the swamp: every creature within 15 feet of it makes a Dexterity saving throw against your spell save DC, taking 4d6 acid damage on a failure and half as much on a success. Anything Restrained cannot move out of the burst.