Perseverant

If an opponent’s attack reduces you to zero HP, you may instead make a Constitution check (DC 15). On a success, you remain at one HP. On a failure, you are reduced to zero HP as normal. You may not make a constitution check if you have exactly one HP, unless the DM says otherwise. You may also not use this against certain attacks or creatures as specified by the DM.

This feat also gives advantage on any ability checks, but only after they have been unsuccessfully attempted at least once.