From Mortal Kombat 3 and onwards, Jax wears a pair of bionic armor-plating that covers and protects both of his arms. It is not known whether his arms were replaced or upgraded in the original story/timeline, however it is possible that he may have used bionic implants until the events of Deception, where he may have willingly had his own arms removed in favor of mechanical replacements.
They started off looking quite simple, being a bunch of bionic armor-plating on both his arms, that have since then become more elaborate and advanced as the series went on.
In Mortal Kombat X, after being turned into a Revenant by Quan Chi, Jax received a heavily modified version of his Bionic Arms, being given a slightly more nefarious design to it with having spikes protruding from the top of the forearms and elbows all the way to his shoulders.
His Bionic Arms return to a more standard appearance upon his restoration from Revenant to Human accompanied by American flags tied around his biceps. During gameplay, his some parts of his arm change in color based on his variations, being the default form with his Heavy Weapons Variation & his variationless form, emitting a blue light in his Pumped Up Variation, and changing to a black-ish color with the lights glowing orange in the Wrestler Variation.
In Mortal Kombat 11, Jax's arms are a part of his Gear items that he could kustomized. With many different designs and variants available for Jax. Not only that, a mechanic that has been added is that every time Jax lands a punch on his opponent, his Bionic Arms begin to slowly heat up until they glow red hot, which have an effect in gameplay.
In the MK 11 Story Mode, Jax is seen with three different Bionic Arm variants. His present version possesses two variants, where he has his standard ones which are then replaced by Bionic Arms of Kronika's design, which give them her sleek white & gold aesthetic alongside some parts seemingly made of out flesh-like materials due to them being the same skin tone as Jax's. His past self possesses arms nearly identical to his appearance in MK3, which while keeping the same appearance are also given an upgrade by the Present Special Forces.
Lieutenant Lance, a non-canon character from the Mortal Kombat: Blood & Thunder comic books. Has a single artificial bionic arm that has the ability to extend his arm a few good meters and the arm has the ability to conduct electricity as well, causing electrical shocks upon contact with an opponent.
Another non-canon comic book character with Bionic Arms is Torque, whom appeared in the Mortal Kombat Special Forces comics. Torque is quite similar to Jax in a way that not only is he muscular member of the special forces but also possesses a pair of bionic arms. Although unlike Jax from that point whom was able to take off his Bionic Arms, had his natural arms replaced with cybernetic prosthetics. He was also notable for constantly increasing the horse power of his arms every time he had maintenance done upon them.
Interestingly, Kano sports a single bionic arm in his cameo during the Bad-Anon meeting in the Wreck-It Ralph movie.
- The Bionic Arms, under the name of Cybernetic Arm, is a Equipment Card in the mobile version of Mortal Kombat. It increases Toughness to all wearers and when equipped on Jax, it gives him a chance to reflects Special Moves of the enemy when they are blocked. When fused to the Tier X, it gives any fighter a chance to reflect back Basic Attack damage back at the opponent.
- They are referred to as Cybernetic Strength Enhancers by Jax in Mortal Kombat: Annihilation.
- Jax's Bionic Arms in MK: Defenders of the Realm and Annihilation were removable revealing biological arms underneath. Interestingly both series also had Jax learning not to rely too much on the strength given to him by said arms.