Phoenix Logs/Banished Units/Infused Engineer
From Halopedia, the Halo wiki
Infused Engineers replace standard Engineers in Voridus' army. They retain the Huragok reconstitution beam but channel large infused gel pools instead of creating overshield bubbles with their special ability.
Extended exposure to the toxic residue of Voridus' experiments with infusion gel has altered his Huragok assistants, causing some to simply fall apart while the rest have been changed in other-more subtle-ways. These "damaged" Engineers are shunned by their healthy companions and display distinctly non-Huragok behaviors, such as a lack of interest in repairing Forerunner machinery and sabotaging equipment of Banished who have annoyed them in the past. As long as the Infused Engineers continue to perform their duties for him, however, Voridus has little interest in their long-term health or new behaviors.