race features:
Child of Mara. You can breathe air and water, and gain swim speed equal to your movement speed. You know Dancing Lights cantrip.
Natural Weapons. Your fanged maw and constricting serpentine body are natural weapons, which you can use to make unarmed strikes.
If you hit with your bite, you deal piercing damage equal to 1d4 + your Strength modifier, and your target must make a Constitution saving throw (DC 8 + your proficiency bonus + your Constitution modifier). On a failed save, the target takes 2d4 lust damage. This attack's damage increases by 2d4 when you reach 5th level (4d4), 11th level (6d4), and 17th level (8d4).
If you hit with your constrict attack, you deal bludgeoning damage equal to 1d6 + your Strength modifier, and the target is grappled (escape DC 8 + your proficiency bonus + your Strength modifier). Until this grapple ends, the target is restrained, and you can't constrict another target.
Serpentine Resilience. You have advantage on saving throws against poison, and you have resistance against poison damage.
Serpentine Build. Having no legs, you cannot wear any form of sleeved leg armor, and magical footwear has to be turned into items you can attach to your tail. However, your substantial weight grants you advantage on saves and checks against being knocked prone and moved against your will.