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  The Kroot are expert jungle-fighters and trackers, and they
  are to be found serving as mercenaries across the Ultima
  Segmentum and beyond. Their integration into the Tau
  Empire requires the Kroot to provide troops to Tau armies
  and furthermore prohibits them from fighting alongside the
  armies of other races.
  Kroot evolution depends on their absorbing the genetic
  traits of other races, selectively inheriting the most
  desirable. They do this through eating specific prey animals
  to ensure the next generation takes on certain
  characteristics of that animal. Unfortunately, the Tau
  insistence that the Kroot fight exclusively for them would
  lead to a disastrous stagnation, so they secretly despatch
  entire armies of mercenaries to fight alongside other races
  in order to expose themselves to genetic material and
  environments not found in Tau space.
  Kroot mercenary armies are led by Master Shapers, who
  lead the band’s Kindreds into every warzone imaginable in
  an effort to gain the abilities of the life forms occupying
  those war-torn areas. Every mercenary band exhibits a huge
  variety of  troops as more and more genetic material is
  absorbed, with the whole of the Kindred using its unique
  abilities to best effect upon the battlefield.The result is that
  each of these mercenary bands develops separately to the
  mainstream of Kroot society. When they periodically return
  to the Kroot home world of Pech, they bring with them a
  wealth of new traits to be absorbed by the race at large.
  KROOT MERCENARIES
  POINTS: 30 + MODELS
  FORMATION:
  3+ of the following units:
  1 Master Shaper (see below)
  1+ Kroot Carnivore Kindred (see Codex: Tau Empire)
  0-3 Knarloc Rider Herds (see Imperial Armour 3)
  0-1 Great Knarloc Pack (see Apocalypse)
  SPECIAL RULES
  Master Shaper: One Shaper in the army must be declared the
  Master Shaper. This individual is steeped in the lore of the race’s
  ancestors, and is able to channel their wisdom and potency
  when attacking his foe. This character is Fearless, counts as a
  psyker, and his close combat attacks count as Witchblade
  attacks (see the special close combat attacks section in the
  Warhammer 40,000 rulebook).
  Headhunters: A Carnivore Kindred not accompanied by any
  Krootox or Kroot Hounds may be upgraded to Headhunters at
  +50 points per unit. All close combat attacks made by
  Headhunters count as poisoned weapons that wound on a 4+.
  Stalkers: A Carnivore Kindred not accompanied by any Krootox
  may be upgraded to Stalkers at +50 points per unit. The unit
  benefits from the Infiltrate, Move Through Cover, Night
  Vision/Acute Senses and Stealth universal special rules.
  Vulturekin: A Carnivore Kindred not accompanied by any Kroot
  Hounds or Krootox may be upgraded to Vulturekin at +50
  points per unit. The unit counts as Jump Infantry, and benefits
  from the Hit & Run universal special rule.
  Hunters: Any kindred in the formation armed with Kroot rifles
  may upgrade these to Kroot hunting rifles for +20 points per
  unit. This changes the rifle’s Type from Rapid Fire weapon to
  Sniper, Heavy 1.
  Hyper Active Nymune Organ: Any unit in the army not
  containing Krootox may be given the Fleet of Foot universal
  special rule for + 20 points per unit.
  VULTUREKIN
  KINDRED
  The Seven Paths Kindred
  CARNIVORE
  KINDRED
  The Silent Step Kindred
  The Wind Stalkers
  MASTER
  SHAPER
  Moonson
  © Games Workshop Limited 2007. Games Workshop, Warhammer, Warhammer 40,000, Apocalypse are ©, TM and/or ® Games Workshop Limited 2007. All rights reserved.
  Thunderfoot
  GREAT
  KNARLOC
  KNARLOC
  RIDER HERD
  
SOURCE: textdata/thevault/Warhammer/40k/1st-8th Editions (Prior)/5th Edition (2008)/Apocalypse Datasheets/40k 5e - Tau - Kroot Mercenaries.pdf