Residuum Propulsion. While the harness is worn and fueled by Residuum, you can use an action to activate it to gain a 60ft flight speed. It is strong enough to propel a Large creature for 1 hour, a Medium for 2, and a Small for 3.

For every hour of flight, roll the Residuum Die (d12) at disadvantage. On a roll of 1, reduce the die by 1 size. When the die is reduced lower than a d4, the harness cannot be used again until refilling it with Stable Residuum, which restores the die to a d12.

Jet Boost. When activated, you can use a bonus action to double the flying speed you gain for one turn, but forces an immediate Residuum Die roll, and you can't use this feature if the Residuum Die is a d4.