X factor

the X factor
(a special quality, especially one that is essential for success and is difficult to describe) — изюминка; харизма; что-то такое особенное, необычно или таинственное (в облике, характере и пр)
Also the x-factor
If someone has the x-factor , they have a certain charismatic appeal and magnetic quality.

Example 1: She certainly has the X factor that all great singers have. (OALD)

Example 2: He's not a great singer but people can't take their eyes off him, so he must have the x-factor. (englishclub.com)

Example 3: You can't teach anyone the x-factor; they've either got it or they haven't. (englishclub.com)

Example 4: Jim's definitely got the x-factor. He's an amazing performer. (englishclub.com)

Example 5: The effect of the weather on production costs is always something of an X factor, or unknown variable.
(OALD)

Related vocabulary:

mojo /ˈmoʊdʒoʊ/ {pl. mojos}
1. a magic spell, hex, or charm; broadly magic(al) power
заговор, магическая формула; волшебство Syn.: spell, charm
2. a small object, or a collection of small objects in a bag, that is believed to have magic powers (талисман, амулет, оберег)
Syn.: amulet, charm, talisman, fetish, mascot
3. the power of someone's attractive personality; self-confidence, self-esteem or sex appeal. — харизма, харизматичность; высокая энергетика (контекст.); внутренняя сила; сексапильность; притягательность, изюминка

Example 1: works his mojo on the tennis court;
Example 2: If you're committed to creating more happiness, meaning and mojo in your life and you know there's more to it than the latest "Secret"/get-it-quick trick, then this class is for you. It'll help you optimize your life so you can live with more health, happiness, meaning and mojo while making a positive contribution to your family, community and world. You'll learn the 10 principles of optimal living and the keys to living with more happiness, meaning and mojo while getting a running start on making 2013 the greatest year of your life.
Example 3:....

Origin
Mojo — a magical charm bag used in hoodoo, which has transmuted into a slang word for self-confidence, self-esteem or sex appeal.