Pack Tactics. The undead monkey has advantage on an attack roll against a creature if at least one of the monkey’s allies is within 5 feet of the creature and the ally isn’t incapacitated.

Undead Fortitude. If damage reduces the undead monkey to 0 Hit Points, it must make a Constitution saving throw with a DC of 5+the damage taken, unless the damage is radiant or from a critical hit. On a success, the undead monkey drops to 1 hit point instead.

Bite. Melee Weapon Attack: +1 to hit, reach 5 ft., one target. Hit: 1 (1d4 – 1) piercing damage.

Fling Poo. Recharge 5-6. The Monkey flings poo at a target within 50 feet. The target must make two saving throws. A DC 12 Dexterity saving throw to avoid being blinded, and a DC 13 Constitution Save to avoid contracting Mad Monkey Fever. 

The infected creature gains a random form of long-term madness (roll on the Long-Term Madness table in chapter 8 of the Dungeon Master’s Guide) that manifests 1d6 hours after infection and lasts for the duration (1d10 × 10 hours). If the madness is allowed to run its full course, the creature must repeat the saving throw at the end of the madness. If the second saving throw fails, the creature suffers another bout of long-term madness (roll again on the table) that lasts for the normal duration. The madness symptoms continue until the disease ends.