The Perfect Jupiter King is the penultimate weapon of the Rebel Army, exclusive to Metal Slug Attack. It first made its debut in the game's mode known as the 'Ultimate Mission', where the boss can also become a playable unit.
"An ultimate weapon developed by the Rebel Army. It is meant to deal a decisive blow that will shift the tide of war, and bring an end to this long drawn-out fierce battle. It has the ability to hasten the attack of all its allies. Gen. Morden and Sergeant Allen are aboard."
- ~Metal Slug Attack in-game description.
The Perfect Jupiter King is a giant mech, based on the Jupiter King. True to its name, it features a much more robotic appearance than its predecessor. Due to the sprites' gigantic size, the upper torso has been cut off screen although it can be seen while performing its special attack or during second form.
In Metal Slug Attack's game mode, it is fought on the Rebel's Ultimate Mission, the boss is not fought until a set time has passed. Once upon deployment, it will be spawned on the player's nearest units while also activating the Rebel's Ultimate Skill, an Attack fever skill which allows the Rebel Army units' special attacks to recharge instantly for a short period of time.
As its primary attack, the Perfect Jupiter King will stomp the enemies with its large foot. For its special, it will charge its fist to punch the ground to deal massive damage. Once upon taking severe damage, the Perfect Jupiter King's legs will be destroyed, leaving the upper torso intact. This prompts Sergeant Allen to use his superhuman strength to lift the mech's body, essentially transitioning to its second form.
In this second form, the Perfect Jupiter King moves rather sluggish but can perform formidable attacks that should not be underestimated. As its primary attacks, it will unleash flurries of punches to deal rapid damage over time. As its special attack, it will use its arm cannon and eye laser against the enemies.
As a playable unit, the Perfect Jupiter King is extremely expensive, requiring immense amount of unit parts to remedy its vast AP cost. Not only its AP but also its unique items which forces the player to spend their sorties for Extra Ops and Guild Ops as its Ultimate Parts can be found there for its skills.