Thorny Terrarium

When evoked the terrarium surrounds your enemies, ensnaring them in a cell of pure thorns.

You may choose a point within range to summon a 20ft cube prison cell made entirely of thorns. At least one side of the cube must be in contact with a solid surface of an appropriate size. The cube requires at least the space of a 20ft cube or the terrarium will not appear. All creatures in the area when the prison appears must make a STR saving throw or be entrapped by your spell.  If the creature makes the save, they are pushed to the outside of the range and are unharmed. At the end of each of its turns, the creature may reattempt the STR save but it increases by 1 each turn as the entrapped becomes bloodier and more carved up.

• Each wall of the prison has an AC of 20 and 100HP. 
  1. Piercing damage including that done to those inside heals the prison by an equal amount as it feasts on the blood of those inside its walls. 
  2. The prison is immune to slashing, piercing and bludgeoning damage from non-magical weapons.
• While inside the prison the entrapped are subject to the following effects.
  1.  All creatures that start their turn inside the prison take 2d8 piercing damage.
  2. Creatures inside are also subject to impaling and as such are considered restrained
     • If the creature is immune to piercing damage the effect does not occur.
  3. The prison serves as partial cover from ranged attacks so all ranged attacks are -2 to hit. 
• As an action, you may end the spell prematurely and cause the terrarium to collapse upon itself in a deluge of impaling thorns and force. By using your action to squeeze your fist together, or any other similar action, you can cause the terrarium to contract upon itself and explode injuring those inside it. This does not occur if the spell is ended due to loss of concentration.
  1. When you cause the collapse all those inside take 4d8 force damage and 4d8 piercing damage. 
  2. For each turn, you concentrate the terrarium begins to grow as it is watered by the blood or ichor of those inside causing more devastation on its collapse. Therefore, for each turn, you concentrate you may add 1d8 piercing and 1d8 force damage to the collapse damage. The increase is added at the start of the turn of the caster of this spell.