They seem to age at the same rate as half-elves but the standard lifespan can far exceed that of their cousins, some and live as long as 155 years.

Most if not all fall in the Neutral or Good category. Very few will fall into despair taking up and evil alignment and inflicting the same torment that they themselves have enduring.

Even though Yuan-ti Halfbreeds are long because of their muscular tail when standing erect, they occupy the same space as most humanoids. Your size is Medium.

Your base walking speed is 30 feet, swimming speed is 20.

Darkvision. Choose two of features that can be chosen, this is one such feature. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.
Poison Resistance. Choose two of features that can be chosen, this is one such feature. You have resistance to poison damage, and you have advantage on saving throws against becoming poisoned.
Magic Resistance. Choose two of features that can be chosen, this is one such feature. You have advantage on saving throws against spells and other magical effects.
Serpentine Empathy. Choose two of features that can be chosen, this is one such feature. You can communicate simple ideas with snakes.
Constrictor Grapple. Yuan-ti halfbreeds can constrict a foe with their powerful tail. Make an unarmed melee attack, on a hit, you deal 1d8 + STR bludgeoning damage, and the target is now restrained. While grappling a creature with your tail you can use both your hands as normal. At the start of their next turn, the target must make a DC 10 + STR saving throw, on a fail they take 1d6 + STR bludgeoning damage and are restrained until the start of their next turn, on a success they do not take damage and free themselves. While restrained, attack rolls done against the target are done with disadvantage. You an not restrained creatures that are larger than you but the will be forced to move at half speed. Increase the damage by one dice at levels 6, 12, 18. (1d8->2d8->etc...) you can use this trait again after a short rest.
Bloodlines. At level 1 you choose one Yuan-ti bloodline.
Languages. You can speak, read, and write in Common, Abyssal and Draconic.

Make an unarmed melee attack, on a hit, you deal 1d8 + STR bludgeoning damage, and the target is now restrained. While grappling a creature with your tail you can use both your hands as normal. At the start of their next turn, the target must make a DC 10 + STR saving throw, on a fail they take 1d6 + STR bludgeoning damage and are restrained until the start of their next turn, on a success they do not take damage and free themselves. While restrained, attack rolls done against the target are done with disadvantage. You an not restrained creatures that are larger than you but the will be forced to move at half speed. Increase the damage by one dice at levels 6, 12, 18. (1d8->2d8->etc...) you can use this trait again after a short rest.

You can speak, read, and write in Common, Abyssal and Draconic.

Tiefling Traits You gain proficiency in one skill of your choice and one Tiefling race or sub-race trait.

Human Traits You gain proficiency in one skill of your choice and You gain one feat of your choice.

Elf Traits You gain proficiency in one skill of your choice and you may pick one Elf race or sub-race trait.

Your Strength score increases by 2. Your Charisma score increases by 1. As normal, you can't increase an ability score above 20 using this feature.