Bloodworm Zombie

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

Blood Worm Infection: These parasites are spread by attacks from a variety of aberrations or stage 4 afflicted individuals who usually are forced to attack others.  The worms enter the bloodstream as extremely small worms, but grow in length to incredible sizes.  The worms consist of eating the blood cells of individuals.  Eventually the worms reach such massive size that they are able to move the body parts of the recently deceased.  They usually then attempt to violently attack others to spread themselves.  The incubation time of bloodworms is 1 week.  This is the time it takes for the disease to progress 1 phase, as well as the time it takes to regress 1 phase.  At the end of each week, the player makes a constitution saving throw DC 15 con saving throw.  If they fail, they progress to the next phase, and if they succeed they regress 1 phase and will continue to regress 1 phase automatically until they are cured.  The symptoms per phase are as follows.

Phase 1:  The worm have reached the bloodstream and start feasting. Individuals usually feel a little tired.  You feel fatigued and fatigued and develop exhaustion twice as quickly.  All rolls to prevent gaining exhaustion are at disadvantage.  

Phase 2:  The worm has grown in size and individuals start feeling very tired.  Occasionally you get an uncomfortable feeling, usually in your hands or feet.  You always have 1 lvl of exhaustion.

Phase 3:  The worm is large enough to feel constantly in your limbs.  Your exhaustion is crippling, to the point that you always have 3 levels of exhaustion.  

Phase 4:  You die due to lack of blood cells.  Immediately after your death, the worm puppets your body to attack others.  Your body becomes a blood worm zombie with hp equal to your max hp. 

To cure someone of bloodworms magically, you must first make a medicine check DC 15 to determine if you have the knowledge required.  One non-magical cure is heat.  If a person takes half their hit points in fire damage per day for a week, they will automatically succeed their con saving throw to determine the disease progression.  This knowledge requires a DC 20 medicine check to uncover.  

If you are ever cured of blood worms, you feel tired for the next month, and occasionally get uncomfortable itches.

Multiattack:  A bloodworm zombie can either make two slam attacks or 1 bite attack per action.

Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (2d6 + 1) bludgeoning damage and the target must make a DC 5 con saving throw or be infected with blood worms.  

Bite.  Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (2d4 + 1) piercing damage and the target must make a DC 15 con saving throw or be infected with blood worms.  

Larval Burst:  When a bloodworm zombie is reduced to 0 hp and fails its undead fortitude roll, the zombie bursts.  Any creature within 10 feet of the zombie must make a DC 5 con saving throw or be infected with blood worms.  In addition, a blood worm swarm takes the place of the now destroyed zombie at full hitpoints.  If the damage that killed the zombie was fire damage, no explosion happens but the swarm still appears.