Your Dexterity, Strength, Intelligence, Wisdom, and Intelligence scores all increase by 2; Constitution is reduced by 7. If before turning you have 9 or less constitution, you die unable to adapt forms.

You have disadvantage on all saving throws.

You are immortal, unable to die by the aches of time, but still susceptible to unfortunate events and premature deaths. Your physical state upon being turned is frozen in time, no longer aging.

Vympari share an evil mindset bent towards their self-preservation. They value both personal freedom and unassuming communities. Demonstrating neither love of leaders nor desire for followers as both tend to cause problems. They chafe at rules, resent others’ demands, and sometimes prove unreliable, or at least unpredictable.

Vympari vary in size according to their birth-race before being turned.
Your eyes over time become harder to hide, changing from their birth color to a yellow, then orange, ending in a bright red.
Your mouth and dentals show no signs of fangs, as the fangs extend as part of the "Fanged Appetite" action. Withdrawing once feeding is finished.

Mortal food is useful only for putting other’s minds at ease. If you haven’t had a blood meal within the last 24 hours before beginning a long rest, you won’t heal. To feed you must use the “Fanged Appetite” action, a successful fanged appetite counts as a blood meal when used against a creature with blood.
You may not use hit dice during a short rest.

Fanged appetite uses charges, starting with 3 at level 1 and gaining 2 additional charges at levels 5, 10, 15, and 20 each. Your fangs are natural weapons, which you can use to make unarmed strikes, the modifier to hit is DEX. If you hit with them, you deal piercing damage equal to 2d6 which you heal* for. This damage increases by 1d6 at level 5, 10, 15, and 20. If you leave the victim alive there is a 5% chance, they will succumb to vymparism during their next long rest, every successive “Fanged Appetite” on the same creature increases this chance by 5%.

* To heal from this attack the target must have blood, against creatures such as constructs, undead, plant-life, etc. you would only do damage and not heal.

Your base walking speed is 40 feet. Uncannily enhanced by your physical prowess.

Thanks to your darkened blood, you have superior vision in dark and dim conditions. 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 have disadvantage on attack rolls and on Wisdom (Perception) checks that rely on sight when you, the target of your attack, or whatever you are trying to perceive is in direct sunlight.

You are immune to both the poison and frightened conditions; and have resistance to the poison damage type.

You gain proficiency in four skills of your choice.

You can speak read and write Common, infernal, and your heritage language. (Language of your choice.)