Strength in Numbers. The mob has a number of maximum hit points equal to the number of members it has multiplied by the hit point maximum of an individual. The number of members may also affect the size of the mob (see below)

• 2-4 members = 2x2 (Large)
• 5-9 members = 3x3 (Huge)
• 10-16 members = 4x4 (Gargantuan)
• 17-25 members = 5x5
• 26-36 members = 6x6
• 37-49 members = 7x7
• 50-64 members = 8x8
• 65-81 members = 9x9
• 82+ members = 10x10

AoE Susceptability. The mob takes 10x damage from effects that target an area, so long as over at least 50% of that area overlaps with the mob. If the mob is subjected to Turn Undead, the mob cannot move closer to the caster, and it has disadvantage on all attack rolls until the end of it's next turn. If the mob is subjected to Destroy Undead, use the group combat rules from the DMG to determine the number of failed saving throws (substituting DC for AC). The mob loses a number of hit points equal to individual HP x the number of failed saving throws - this damage cannot be reduced in any way.

Swarm. The mob can occupy another creature’s space and vice versa, and the mob can move through any opening large enough for a Medium humanoid. The mob cannot gain temporary hitpoints, and can only regain hit points with the addition of new members.

Chaotic. The area the mob occupies is considered difficult terrain for large or smaller creatures. In combat, the mob gets a reaction that it can take once on every creature’s turn. It can use this reaction only to make an opportunity attack, and creatures provoke an attack of opportunity when they move 5 or more feet within the area the swarm occupies.

Undead Fortitude. Any time the mob takes damage it must make a constitution saving throw equal to 5 + the damage taken, unless the damage was radiant or came from a critical hit. On a success, the damage that the mob takes is halved. The easier calculation is to roll a saving throw equal to the damage taken, but with a -2 modifier - this is a DDB rollable notation for that.

Multiattack. Calculate the number of remaining members of the mob based on its current hit points (current HP/individual HP, rounded up). It can make a number of attacks equal to this number, with a maximum attacks to an individual being based on the individuals size (see below). Use the group combat rules from the DMG if necessary.

• Medium: 8
• Large: 12
• Huge: 25
• Gargantuan: 36

Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target occupying the same space as the mob. Hit: 4 (1d6 + 1) bludgeoning damage.