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 as the games went on.
In Mortal Kombat X, after being turned into a Revenant by Quan Chi, receiving 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 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 now 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 whivh are then replaced by Bionic Arms of Kronika's design, which also seems to have parts made of flesh 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.
- 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.