Corrupted Treant Heart
Wondrous item, very rare (requires attunement by a Druid)
This twisted and blackened wooden heart is strung through with thorny vines and worn as a pendant.
Thorns dig into your neck while you are attuned to this magical item, reducing your hit point maximum by 5. Your skin develops a black and spiny bark-like appearance and you gain the benefit of the barkskin spell (doesn’t require concentration). Additionally, creatures that hit you with melee attacks take 1d4 piercing damage.
As an action you can cause a surge of thorns to erupt from the ground in a line 5 feet wide and 60 feet long. Any creature on the ground that is caught in this area must make a Dexterity saving throw against your spellcasting DC. On a failure they take 8d4 piercing damage and their walking speed is halved until the start of your next turn. On a success a creature takes half damage and its walking speed is not halved. You can't use this property again until you finish a long rest.