Sergeant Chronus

When adding Sergeant Chronus to your army, you must also take a single Rhino, Razorback, Predator, Whirlwind, Vindicator, Hunter, Stalker, Land Raider, Land Raider Crusader, or Land Raider Redeemer, payin gthe points cost listed on that vehicle's datasheet as well as the 50 points for Sergeant Chronus.  The chosen vehicle is a Character and has Ballistic Skill 5.  In addition, it has the It Will Not Die special rule and ignores the effects of Crew Shake and Crew Stunned results.

If the tank is Wrecked or suffers an Explodes! result, Sergeant Chronus is treated as a passenger.  (Note that if the vehicle does not have an Access Point, he will have to perform an emergency disembarkation).  Assuming Sergeant Chronus survives his vehicle's destruction, he uses his own characteristic profile and special rules as normal from that point on.

When choosing an army, all models in the same Detachment or Formation must be drawn from the same Chapter.  If a unit's datasheet contains a Chapter in brackets after the Chapter Tactics special rule - for example, "Chapter Tactics (Ultramarines)" - the unit must always be drawn from this Chapter, and therefore cannot be included in a Detachment or Formation with any units that are drawn from other Chapters. All models drawn from a given Chapter benefit from that Chapter's Special Rule. If a unit contains models drawn from two different Chapters, it counts as from neither Chapter, and thus benefits from neither Chapter Tactic.

A unit that contains at least one model with this special rule automatically passes Fear and Regroup tests. When it Regroups, the unit does not make the 3" Regroup move, but can instead move, shoot (or Run) and declare charges normally in that turn. Furthermore, if a unit containing one or more models with this special rule is caught by a Sweeping Advance, they are not destroyed, but remain locked in combat instead.

Independent characters can join other units.  They cannot, however, join units that contain vehicles or Monstrous Creatures.  They can join other Independent Characters, though, to form a powerful multi-character unit!  Independent Characters pass Look Out, Sir rolls on a 2+. A unit that contains one or more Independent Characters does not need a double 1 to Regroup if reduced to below 25% of its starting numbres, but instead tests as if it had at least 25% remaining.

Full details in BRB. Rule too long to copy verbatim.

At the end of each of your turns, roll a D6 for each of your models with this special rule that has less than its starting number of Wounds or Hull Points, but has not been removed as a casualty or destroyed. On a 5+, that model regains a Wound or Hull Point lost earlier in the game.