Carnage Maw. Each time the Z-rex damages an organic creature with its bite attack, it gains a +1 bonus (stacking) to its necrotic damage, up to a max of 5. This bonus resets after 1 hour, after which the festering gore of its victims slaws of its teeth.

Stench. Any creature that starts its turn within 10 feet of the Z-rex must succeed on a DC 14 Constitution saving throw or be poisoned until the start of its next turn. On a successful save the creature is immune to the Z-rex's stench for 24 hours.

Undead Fortitude. If damage reduces the Z-rex to 0 hit points, it must make a Constitution saving throw with DC 5+damage taken, unless the damage was from radiant or a critical hit. On a successful save, the Z-rex drops to 1 hit point instead.

Multiattack. The Z-rex makes 2 attacks 1 with its bite and 1 with its slam. It can't make both attacks against the same target.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., 1 target. Hit: 20 (2d12 + 7) piercing damage plus 13 (2d12) necrotic damage. If the target is an organic creature, it must make a DC 14 Constitution saving throw or become infected. An infected creature takes a -1 penalty to all rolls they make. The creature can repeat the save at the end of their turn, if they fail the penalty goes up by 1 to a max of 5.

Slam. Melee Weapon Attack: +10 to hit, reach 10 ft., 1 target. Hit: 20 (2d12 + 7) bludgeoning damage. Target must make a DC 17 Strength saving throw or be pushed back 10 ft., and be knocked prone. The Z-rex and choose to make this attack reckless, giving it advantage on the attack. If it uses reckless the next attack against the Z-rex has advantage.