[Undead Fortitude]: If damage reduces Chippers to 0 Hit Points, he must make a Constitution saving throw with a DC of 5+ the damage taken, unless the damage is radiant or from a critical hit. On a success, Chippers drops to 1 hit point instead.
Bite. Melee Weapon Attack: +0 to hit, reach 5 ft., one target. Hit: (1d1) piercing damage. Keen Smell. Chippers has advantage on Wisdom (Perception) checks that rely on smell.
Chippers is a tiny undead mouse, given to Adelaide Bridger by the necromancer Hamun Kost. The mouse was Kost's childhood pet, and the first creature he ever reanimated.