Rage. Once per short rest, the Zomboss can burst into a rage.  Raging adds +4 to the Zomboss' Strength Modifier and a +4 damage bonus to any bludgeoning attacks.  Rage also gives the Zomboss a 50% resistance to bludgeoning, piercing, and slashing attacks.     

Lunge. The Zomboss can lunge forward, moving up to 20 ft. plus the Athletics check value.  If a player is in the path of its lunge, that player takes the same damage as its Slam Attack.     

Slam. Melee Weapon Attack: +10 to hit, reach 10 ft., 3 targets. Hit: 2 (1d12 + 7) bludgeoning damage. 

Mega Punch. Melee Weapon Attack: +8 to hit, reach 7 ft., 1 targets. Hit: 2 (1d8 + 9) bludgeoning damage. 

Throw Rock. Ranged Weapon Attack: +8 to hit, range 20/50 ft., 1 target. Hit: 2 (2d6 + 5) bludgeoning damage.

Tank. When this monster is attacked by a non-magical attack, it can make a Strength saving throw.  If the saving throw value is higher than 16, the monster gets a 25% resistance to the attack.