Undead Fortitude. If damage reduces the zombie ball 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.

Rolling attack. When it rolls at least 35 feet towards a target then hits the target with an attack the attack does an extra 6(2d6) damage.

Zombies Combined. The zombie ball can fit through openings small enough for a medium zombie when it does this the zombie ball splits apart and has the statistics of 10 normal zombies until it takes an action to reform into a zombie ball.

Slams. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 40 (10d6 + 10) bludgeoning damage, or 20 (5d6+5) bludgeoning damage if the zombie ball has half of its hit points or fewer.