Mithroden

At first the sword seems to be a normal +3 long sword. But once the blade witnesses a eclipse it awakens for the next 100 years.
Awakened State:
-During the time when the sun is out the blade does 1d8 extra radiant damage.
-When the moon is out the blade does 1d8 extra necrotic damage.
-The player heals for the amount equal to the extra damage no matter the time of day.