Undead Fortitude. If damage reduces the rat to 0 hit points, it 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, the rat drops to 1 hit point instead.
Bite. Melee Weapon Attack: +0 to hit, reach 5 ft., one target. Hit:1 piercing damage.
Ghoulcallers are necromancers—mages who use black mana to call forth the dead from graveyards. These risen dead are called ghouls, or the unhallowed. The ghoulcaller fills the fragile mind of his or her creation with a single driving purpose, which the ghoul carries out to the best of its ability using whatever skills it has. The result is a grotesque parody of life: risen blacksmiths attempting to "reforge" their opponents, fallen warriors rasping incoherent battle cries, undead murderers…