Regen-inf troops were members of the lesser species who were biologically modified by the Great Houses to fight in the War in Heaven. Like the Third Wave, regen-inf were given the ability to regenerate into bodies with built-in weapons. The name was a contraction of the words "regeneration" and "infantry".
While some regen-inf kept humanoid forms, most attained gigantic bodies which were "not even remotely recognisable" as living things. (PROSE: The Book of the War) As time progressed, they would build up layers of "high-technology scar tissue": (PROSE: Dead Romance) thick ablative armour with microscopic torpedo tubes as pores. (PROSE: The Book of the War) Christine Summerfield described one regen-inf soldier as looking like a knight in armour with tank parts for limbs. (PROSE: Dead Romance)
Regen-inf soldiers were also mentally changed to fight in the War. They were given time-awareness and some of their brain structures became dimensionally extruded. Many advanced regen-inf had psychological or even physical self-destruct protocols implanted through briefings; some displayed physical responses to the conditioning, like stigmata and death's-head imprints on the skin. (PROSE: The Book of the War)
Father Kreiner collected the severed heads of several members of the "lesser races" who been genetically modified by the High Council to have Time Lord-like abilities for use in the War. (PROSE: Interference - Book One)
In the City of the Saved, regen-inf soldiers were politically represented by House Halfling. Verrifant, a former regen-inf, served as Lord Mayor of the City of the Saved for a couple years. Some regen-inf lived in the Ghetto of the Damned. (PROSE: The Book of the War)