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 from a critical hit. On a success, the zombie drops to 1 hit point instead.

Still as Stone: Zombie dwarfs can hide as boulders before adventures enter the room or cave. They can launch 1 surprise attack with advantage. players must make a perception check with DC of 15 to prevent surprize attack.