Ravager

Each time a model in this unit makes an attack with a melee weapon, on an unmodified wound roll of 6, improve the Armour Penetration characteristic of that attack by 1.

Battle Round 1+ - Inured to Suffering: Models in this unit have a 6+ invulnerable save.
Battle Round 2+ -  Eager to Flay: This unit is eligible to declare a charge in a turn in which they Advanced.
Battle Round 3+ -  Flensing Fury: Each time a model in this unit makes a melee attack, add 1 to that attack's hit roll. If this unit has the VEHICLE or MONSTER  keyword, it does not suffer the penalty incurred to its hit rolls for firing Heavy weapons at enemy units that are within Engagement Range of it.
Battle Round 4+ -  Mantle of Agony: Models in this unit have a 5+ invulnerable save.
Battle Round 5+ -  Emboldened by Bloodshed: Each time a Morale test is taken for this unit, it is automatically passed. If this unit's characteristics can change as it suffers damage, this unit is considered to have double the number of wounds remaining for the purposes of determining what those characteristics are.