For lack of any real name, this technique has been dubbed 'mystic' by all those to have seen it; due largely to its 'mystical' nature. Different from all other sorts of powerlevel increasing techniques and transformations, this skill works by giving a person a profound understanding of their own power, enabling them to draw out part or all of their hidden powers at will.
However, learning this technique comes at a cost. By learning to control ones powers in such an effortless, serene way, they lose the ability to use any other form of powerlevel increase they knew. But it is not a permanent loss. If someone decides they no longer wish to know this way of fighting, they can release the powers of Mystic from their bodies and regain control over their previous power increasing abilities. It can only be taught to someone by the Grand or Supreme Kaioshin (not the imm kaioshins). Kaios have this skill naturally, as it is a part of their training as a Kaio, so they are exempt from this rule.
Mystic works similar to the Super Namek ability, in that it is a modular skill. You are able to choose to go to a pl mod between 1 and 30; each mod increasing all of your stats by that amount (ie, mystic x30 = +30 to all). Each 'step' requires an additional 250 energy to use. So at max, it requires 7500 energy. Mystic requires a powerlevel of 100 billion to be learned. Kaios and Kaio-K fusions, however, can learn Mystic at 2 billion powerlevel. Like Super Namek, you can go up and down in mods while in mystic at will, simply by typing Mystic (mod#). To power down from Mystic, you can either type Powerdown, or Mystic 0.
The following races can learn Mystic:
Saiyan (including Saiyan-S, Saiyan-T, Saiyan-HB, Saiyan-N)
Halfbreed (including Halfbreed-HB, Halfbreed-S, Halfbreed-T, Halfbreed-N)
Terran (including Terran-T, Terran-S, Terran-HB, Terran-N, Terran-G)
Namek (including Super-Namek, Namek-S, Namek-HB, Namek-T)
Kaio (including Kaio-K)