They are moves that cause a large amount of damage, comparable to "Super Moves" found in various other fighting games. True to their name, these moves consist of a short sequence of attacks that zoom in on the target with an X-Ray and displays bones and organs being crushed, smashed, ruptured, and snapped, dealing massive damage. The player must completely charge up the Super Meter(which also includes various of more minor super moves) in order to perform an X-Ray Move.
While incredibly powerful, a few X-Ray Moves require special conditions to be met. For example, Johnny Cage (MK2011) and Sonya Blade (MKX) both have X-Ray Moves that are classified as a counter-attack, meaning that it is only performed if they are attacked within a few seconds of the player activating it. Other limitations include X-Ray Moves that can only be activated from an aerial position, such as Cyber Sub-Zero (MK2011), Takeda (MKX), and Tanya (MKX) and the fact that the damage inflicted by an X-Ray is altered based on the damage scaling.
In Mortal Kombat X Mobile, X-Ray attacks are unblockable and deal extreme damage and a Buff (to the user) or a Debuff (to the opponent) and is activated from a Gold or Diamond character in the game. X-Rays cannot be activated by Bronze or Silver characters. It takes all 3 Bars of Power for a Gold or Diamond character (Konqueror Shao Kahn can start with 4 Bars of Power if geared with his Helmet and Wrath Hammer) to perform their X-Rays.
A buff on an X-Ray for example is when Johnny Cage, Kung Lao, Leatherface and Kano's X-Rays give Strength to themselves and to their teammates. Other buffs include Regen (regenerates health), Dispel (removes debuffs), Shield (increases defense), Luck (increases critical chance) and Power (increases power generation).
A debuff on an X-Ray for example is when Jason Voorhees, Mileena, and Baraka deal Bleed DOT to the opponent. Other debuffs include Fire (DOT that slowly drains power), Curse (opponent deals more critical damage), Weaken (reduces opponent damage), Blind (makes attacks miss), Power Drain (drains opponent's power) and Cripple (prevents opponents from using a special attack).
In MK11, X-Ray moves has been replaced with Fatal Blows although they have similarities, it can only be access if the player is in low health.
Johnny Cage, Kung Lao, Leatherface and Kano: Strengthen
Quan Chi: Dispel
Sonya Blade, Sub-Zero, Ermac, Tremor and Shao Kahn: Shield
Balanced Kenshi, Takeda and Erron Black: Luck
Raiden, Other Kenshis, Goro, Kintaro, and Jax Briggs: Power
Baraka, Mileena and Jason Voorhees: Bleed
Liu Kang and Freddy Krueger: Fire
Scorpion, D'Vorah, and Shinnok: Curse
Kotal Kahn and Triborg: Weaken
Kitana, Kung Jin, and Jade: Blind
Cassie Cage: Power Drain
Jacqui Briggs, Tanya and Bo' Rai Cho: Cripple