Any friendly unit of Monstrous Infantry, Monstrous Cavalry, Monstrous Beasts or Monsters within 12" of one or more models with this special rule gains the Regeneration (6+) special rule.
Source: Warhammer Armies Project: Unofficial 9th Edition
Any friendly unit of Monstrous Infantry, Monstrous Cavalry, Monstrous Beasts or Monsters within 12" of one or more models with this special rule gains the Regeneration (6+) special rule.