Hydra

Charge Range rolls made by units entirely with Scent of Blood gain Maximised if the target of the Charge contains a Health Pool that has fewer Health Points than its starting value.

Units containing Solitary can never join other units, and can never be joined by other models.
Note: if a model has both Solitary and Attached, it cannot be Deployed and is therefore considered a casualty.

Rolls for Charge Range, Flee Distance and Pursue Distance by units entirely with Swiftstride gain Maximised.

When a unit containing Terror declares a Charge in the Charge Phase, the target must take a Panic Test. If the test is failed, the unit must choose Flee! as its Charge Reaction if allowed to do so (e.g. not already Engaged in Combat, etc.).
Units containing Terror are themselves immune to the effects of Terror.

Regeneration is a Special Save, with a value indicated in brackets (X).
If X is given as a modifier and with a maximum value (e.g. +2), the model gains this as a modifier to all its Regeneration Special Save rolls, which can never be increased to rolls better than 3+. If the model does not have Regeneration, it instead gains Regeneration (7 X+). For example, a model without Regeneration that gains Regeneration (+2) will gain Regeneration (5+).
Note that Regeneration Saves cannot be taken against attacks with Flaming Attacks, nor against attacks with Lethal Strike that roll a ‘6’ to wound.

During its First Round of Combat, any model part with First Strike, or using a weapon with First Strike, gains the Rules and Characteristic modifiers stated in brackets.
For example, a model part with First Strike (+1 Str) gains +1 Str in its First Round of Combat.

Whenever the model loses a Health Point, it gains +1 Att.
Whenever it Recovers or Raises a Health Point, it suffers −1 Att

A model part with Stomp Attack can make a Special Attack which is resolved at Agility Step 0, can only be allocated towards a Health Pool of Height 0–1, and inflicts X hits, using the model part’s Strength, Armour Penetration and Attack Attributes, but not Weapons. If more than one model part of a combined model has Stomp Attack, only a single model part (chosen by the model’s owner) can perform its Stomp Attack in each Round of Combat.

Whenever an attack with Poison Attacks hits with a to-hit roll of ‘6’, it wounds automatically (no to-wound roll needed).
If the attack has two or more instances of Poison Attacks, it wounds automatically on a successful to-hit roll of ‘5’ or ‘6’ instead.
If the attack is turned into more than one hit (e.g. a hit with Area Attack or Fury), only a single hit, chosen by the attacker, wounds automatically. All other hits must roll to wound as normal.

During Combat Choices a model part can only choose a Hand Weapon if it has no other options, or is a Weapon Master.
Models with a Shield using a Hand Weapon gain Parry.
All model parts without Innate Weapons come equipped with a Hand Weapon as their default equipment and cannot lose it.

During Combat Choices a model part can only choose Innate Weapons if it has no other options.
All model parts with Beast, Construct, or Mount come equipped with Innate Weapons as their default equipment and cannot lose them.