While the focus of D&D is always on individual heroes and small groups of adventurers, some scenarios call for large-scale warfare and clashes of kings and their armies, and in a world with necromancy you had better believe that the armies of darkness will find a way to combine the two with a terrifying twist.
Note: This item uses the base 5E rules for siege weapons as well as the greatly expanded rules for such items and mass combat in Ultimate Kingdoms from Legendary Games.
Siege Shot, Zombie Apocalypse
Weapon (ammunition), very rare
This mass of corpses is lashed together and imbued with dreadful necromantic power before being launched in a grotesque bombardment.
Zombie Squad. Ranged Weapon Attack. +5 to hit, range 200/800 ft. (mangonel) or 300/1,200 ft. (trebuchet), all targets in a 15-ft. square. Hit: 22 (4d10) bludgeoning damage, and all creatures in the area must make a DC 13 Constitution saving throw. On a failed save, the creature contracts zombie rot. While it has zombie rot, the creature cannot regain hit points except via magical means, and it has vulnerability to slashing damage as its flesh rots. At the end of each long rest after being infected, the creature’s maximum hit points are reduced by 3 (1d6) and it can repeat the saving throw, ending zombie rot on a success. Any reduction to the creature’s hit point maximum is permanent until the zombie rot has been cured. The reduction ends after the creature’s next long rest after being cured. If this reduction drops the creature to 0 hit points, the creature dies and rises as a plague zombie (see the Tome of Horrors from Frog God Games) in 1d4 hours.
In addition, after striking, the zombie siege shot breaks apart into a gang of 10 plague zombies which attack all living creatures nearby. These zombies turn to dust when they reach 0 hit points or after 1 minute, whichever comes first.
Ultimate Kingdoms Rules. When used to perform a plague bombardment during the Ranged Phase, during the Melee Phase the corpses animate as 20 zombies. These zombies are treated as a temporary platoon (see Table 3-5: Army Size and Statistics) with ACR 4 that attacks for one Battle Phase and then is automatically destroyed. In addition, if the apocalypse zombies damage an army with their melee attack, the kingdom's Stability check to resist that army contracting disease takes a -4 penalty and the chance of a Plague event in the city is increased to 25%.