Ring of Misty Step

Ring, very rare (requires attunement) This silver ring some kind of magical shadowy substance inside. Each has 4 charges and allows you to cast the misty step spell (as a bonus action), the magical shadowy substance inside disappears. Every Midnight, 1d4 charges are replenished.
Possessing this ring comes with a gamble. When you cast the misty step spell, you must roll a 1d20. Down below is the list of outcomes, depending on what is rolled.
If you roll a:
1. You successfully cast misty step, but to a random location within 10ft decided by your DM.
2. Nothing Happens, the spell does not work and the crystal stone depletes.
3-7. You successfully cast misty step, but as you reach your destination, you take 1d4 of Force damage.
8-18. You successfully cast misty step, you reach your destination.
19. You successfully cast misty step, as you reach your destination, heal 1d4 HP. (Add 1d4 to Temporary hit points if HP if at max)
20. You successfully cast misty step, as you reach your destination, a crystal stone does not deplenish