As a neutral unit, the Hill Troll Priest can attack while healing. However, this attacks act like melee attacks (hit instantly, cant be avoided).

  1. Find a small troll camp
  2. kill the 2 non-healing trolls
  3. damage the healing troll
  4. move back a bit and watch

Result: The healing troll heals and attacks at the same time, which is fine. However, the attacks while healing act like melee attacks. They are instant, cant miss to uphill and trigger things which melee attacks trigger