When a true Yuan-Ti is in presence of gold and / or treasures such as precious jewels, it must make a WIS saving throw. 

On a success, the Yuan-Ti keeps his or her lust for gold in check. On a failure, the Yuan-Ti is uncontrolably attracted to the gold or treasure and will try to take possession of it by any mean necessary, disregarding social cues and better judgement. If someone already owns said treasure, the Yuan-Ti will try to persuade the owner to give it to him but if he refuses he will use his natural magic to charm him. In extreme cases, the Yuan-Ti will use brute force to claim the treasure.

The DC of the save will be higher depending on the amount of treasure and / or rarity of it

Additionally, a true Yuan-Ti has disadvantage on Insight checks related to trying to assertain whether someone is telling the truth or being trustworthy if said person is using money or treasure as an argument.

Your Strenght score increases by 2, and your Charisma score increases by 1.

Yuan-Ti Abominations can live for 200 years.

True Yuan-Ti are faithful to their tribe and culture. They tend to be Lawful.

True Yan-Ti are taller and larger than other Yuan-Ti and human-like creature. Your size is considered Large.

Your base walking speed is 30 feet.

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.

You know the poison spray cantrip. You can cast animal friendship an unlimited number of times with this trait, but you can target only snakes with it.

Starting at 3rd level, you can also cast Suggestion as a bonus action when you're playing a flute, after casting it, you can't do so again until you finish a short rest. Once you cast it, you can’t do so again until you finish a long rest.

When you reach 5th level, you can cast polymorph but only into a large constrictor snake or back to your true form. You cannot cast any spells as the giant snake and once you cast it, you can't do so again until you finish a long rest.

Charisma is your spellcasting ability for these spells.

You have proficiency in Perception.

You are immune to poison damage and the poisoned condition.

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

You have sharp snake fangs, which are natural weapons you are proficient with. They deal 2d4 piercing damage + your STR modifier.

Using your snake body you can easily maneuver around enemies and wrap around them. With this trait you have advantage on all your grappling checks.