Necklace of Adaptation

Wondrous Item, Uncommon (Requires Attunement)

While wearing this necklace, you can breathe normally in any environment, and you have

If you have Advantage on a D20 Test, roll two d20s, and use the higher roll. A roll can't be affected by more than one Advantage, and Advantage and Disadvantage on the same roll cancel each other. See also D20 Tests.

on saving throws made to avoid or end the

While you have the Poisoned condition, you experience the following effect.

Ability Checks and Attacks Affected. You have Disadvantage on attack rolls and ability checks.

condition.

Source: Dungeon Master's Guide, p. 280