Kastus's Dark Gift

Unwelcome Words. You can speak, read, and write Sylvan and Druidic.
  Sapping Touch. When you deal necrotic damage to a creature, you regain hit points equal to half your level, rounded down (minimum of 1).
  Corrupting Influence. Immediately after you make an attack roll, an ability check, or a saving throw and roll a 1 on the d20, the inky tendrils in your veins surge through your body and penetrate your mind. The next time a friendly creature within 30 feet of you makes an attack roll or casts a spell, roll a d4. If the result is a 1, the attack misses or the casting fails. Once this effect occurs, it can't happen again until you finish a short or long rest.