Magic Resistance. The yuan-ti mummy has advantage on saving throws against spells and other magical effects.

Innate Spellcasting. The yuan-ti mummy's innate spellcasting ability is Charisma (spell save DC 15). The yuan-ti can innately cast the following spells, requiring no material components:

At will: animal friendship (snakes only)
3/day: suggestion 
1/day: fear, animate dead

Aura of Rot. If the yuan-ti mummy damages a creature within 5', it must succeed on a DC 14 Constitution saving throw or be cursed with mummy rot. The cursed target can't regain hit points, and its hit point maximum decreases by 10 (3d6) for every 24 hours that elapse. If the curse reduces the target's hit point maximum to 0, the target dies, and its body turns to dust. The curse lasts until removed by the remove curse spell or other magic

Multiattack. The yuan-ti mummy  The yuan-ti mummy can use its Dreadful Glare and makes two melee attacks, but can use its constrict attack only once.

Scimitar. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) slashing damage plus 7 (2d6) necrotic damage.

Constrict. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 4) piercing damage plus 7 (2d6) necrotic damage, and the target is grappled (escape DC 14). While the target is grappled it takes 7 (2d6) necrotic damage at the end of each turn. Until this grapple ends, the target is restrained, and the yuan-ti mummy can't constrict another target.

Dreadful Glare. The yuan-ti mummy targets one creature it can see within 60 ft. of it. If the target can see the mummy, it must succeed on a DC 14 Wisdom saving throw against this magic or become frightened until the end of the mummy's next turn. If the target fails the saving throw by 5 or more, it is also paralyzed for the same duration. A target that succeeds on the saving throw is immune to the Dreadful Glare of all mummies (but not mummy lords) for the next 24 hours.