Cryo Troopers replace Hellbringers in Serina's combat force. Fury runs hot and cold, as evidenced by Serina's plans for a cadre of cryotech—equipped infantry. Cryo Troopers are armed with a portable cryo spray which deals damage and inflicts a chilling effect on enemy units. This can shut down enemy vehicles and structures [including turrets], temporarily shutting them down even if they are not subsequently shattered. They can be upgraded with advanced cryo systems, which increases the damage, range, and area covered by the chilling field of their spray.
Hellbringers are qualified to maintain, operate, and deploy a number of specialist weapon systems in the UNSC arsenal. This includes a range of incendiary, thermobaric, energetic, chemical, and biological weapons that most UNSC personnel are not even aware of. Serina reasoned their hazardous material qualifications and daredevil reputation made them well—suited for field testing experimental cryotech weaponry. Who better to strap on experimental and unstable power cells that tap strange energies than Marines who routinely wear volatile chemical packs into battle? She was probably right, if the spirited discussion about her cryotech weapon templates among the Spirit of Fire's Marines is any indication.