Briar Bastion

A defensive hedgerow of thorny rose-briar springs forth from the ground. You can choose to have the barrier form a wall up to 30 feet long and 5 feet tall, or a circle that is 15 feet in diameter and 10 feet tall. In either formation, the vegetation is 5 feet thick, providing three-quarters cover, and creatures on both sides of it are heavily obscured. A creature that enters the briar for the first time on its turn or starts its turn inside must make a Dexterity saving throw. On a failure, it takes 3d4 piercing damage and its speed is reduced to 0 until the start of its next turn.