Hydra

All Tyranid units change their [Hive Fleet] keyword to Hydra. All units with the Hydra Keyword gain the Allegiance: Hydra special rule. The Allegiance: Hydra special rule consists of the following rules:

• The Swarm: At the start of combat, at initiative step 10, if a Hydra Hormagaunt Brood, Ripper Swarm, or Termagant Brood unit has more models in its unit than enemy models in all engaged units, they gain +1 to their Weapon Skill (WS) characteristic. Ripper Swarms models count as 4 models for this special rule.
• The Many Headed Beast: A Hydra army must have 3 Troops choices for every 1000pts.