Ultimate Sub-0 is the evolved form of Sub-0. He is voiced by Max Mittelman.
Ultimate Sub-0 is a blue and aqua metallic alien, with a spheroid body. He has two containers with liquid nitrogen on his head and has black mask-like markings around his red eyes. He has two tubes of liquid nitrogen reaching from a respirator (with a dry ice center) where his mouth should be to his back, and his forearms are filled with liquid nitrogen. He has aqua three-fingered hands and two black toes on each foot. Ultimate Sub-0 wears the evolved Simplicitrix symbol on his chest, which has growths in the shape of "S" and "0" on it, referencing the initials of "Sub-0."
- Ultimate Sub-0 retains the powers of his previous self.
- Ultimate Sub-0's powers come from the liquid nitrogen flowing through his body. He can shoot the nitrogen with extreme pressure, using it as a projectile. The vapor of the nitrogen can be used to help him escape situations. His liquid nitrogen is so instantaneous that it is able to freeze fire. It does so by freezing the energy and matter of the fire, as well as its source, almost simultaneously. This ability allows him to easily fight Pyronites and Vespernans by freezing them. Ultimate Sub-0 can even revert glass into sand.
- Ultimate Sub-0 can manipulate air pressure.
- Combining his cyrokinetic powers and air pressure manipulation, Ultimate Sub-0 can create dry ice and control it. The range of how much dry ice he can make is limited to how far he can shoot his liquid nitrogen in an area of air pressure he is manipulating.
- Ultimate Sub-0 is more metallic than Sub-0, making him more durable.
- Ultimate Sub-0 lacks the container on his back that Sub-0 had, making him faster and more agile.
- Ultimate Sub-0's metal containment suit makes him much more stable than the suit of Sub-0, lowering the risk of accidentally freezing anyone. This means the Ultimate Form is actually safer to use than the original. The suit also has minor artificial intelligence, being able to tell the difference between friend and foe.
- Ultimate Sub-0's metal suit is weak to magnetic and electric opponents.
- Ultimate Sub-0's powers are useless against enemies immune to ice.
- Ultimate Sub-0 uses the design of Overflow from the Ben 10 Reboot. Interestingly, Ultimate Sub-0's color scheme is similar to that of Water Hazard from Richard 10, and Overflow is the Reboot's "equivalent version" of Water Hazard.
- The theoretical science for Ultimate Sub-0's ability to freeze fire was based on Aaronbill3's response to Alan asking on the Discord how to freeze fire.