Undead fortitude. If damage reduces the zombie 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 a critical hit. On a success, the zombie drops to 1 HP instead.
Slam. Melee Weapon Attack. +3 to hit, reach 5 ft, one target, 1d6+1 bludgeoning damage.