Amulet of Focus

When you are concentrating on a spell, this amulet allows you to use your reaction to 'attach' that focus to the amulet when you cast a new spell that requires concentration. The first spell no longer requires you to concentrate on it for the duration unless you are no longer concentrating on the second spell, at which point the first spell is no longer 'attached' to the amulet. While the first spell is 'attached' to the amulet, you only need to make concentration checks to maintain the second spell when you take damage. When you lose concentration on the second spell, or its duration completes, you resume concentrating on the first spell. This feature can only be used once per long rest.