Venomous Mummy

Toxic Smoke. If the venomous mummy takes fire damage, each creature within 10 feet of it must make a DC 12 Constitution saving throw as its venom-soaked wraps emit a poisonous smoke. On a failure, a creature takes 7 (2d6) poison damage and is poisoned until the end of its next turn. On a success, a creature takes half the damage and isn't poisoned. The smoke fills a 10-foot-radius sphere centered on the mummy. The sphere spreads around corners, and its area is lightly obscured. It lasts until the end of the mummy's next turn. A creature that enters the cloud for the first time on a turn or starts its turn there is poisoned until the end of its next turn.

Venom-Soaked Wraps. A creature that touches the mummy or hits it with a melee attack while within 5 feet of it takes 3 (1d6) poison damage.

Undead Nature. The venomous mummy doesn't require air, food, drink, or sleep.

Venomous Fist. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage plus 10 (3d6) poison damage. If the target is a creature, it must succeed on a DC 12 Constitution saving throw or be cursed. Every 24 hours that elapse, the cursed target must succeed on a DC 12 Constitution saving throw or take 7 (2d6) poison damage, and its hp maximum is reduced by that amount. This reduction lasts until the target finishes a long rest after the curse is removed. The target dies if this effect reduces its hp maximum to 0. The curse lasts until removed by the remove curse spell or similar magic.