Impact (X) "On a successful Charge, a Model with the Impact (X) Special Rule temporarily increases a Characteristic by 1."
If a Unit that includes any Models with the Impact (X) Special Rule or any Models that have any Weapons with the Impact (X) Special Rule, and that Unit makes a successful Charge, then this Special Rule is triggered. Once triggered, until the end of that Assault Phase, when making Melee Attacks for Models in that Unit, each Model or Weapon that is selected for one of those Models, that has a variant of this Special Rule, gains a modifier of +1 to any Characteristics that is the value of X.
Heedless "A Unit that includes any Models with this Special Rule cannot claim Objectives."
A Unit that includes any Models with this Special Rule cannot Control or Contest any Object Marker - this overrides any other Rule or Special Rule that may apply to the Unit regardless of the source of the Rule or effect.
Bulky (X) Models with the Bulky (X) Special Rule take up more space on Transport Models."
A Model with the Bulky (X) Special Rule does not use up 1 Point of Transport Capacity when it Embarks on a Model with the Transport Sub-Type. Instead it uses up a number of points of Transport Capacity equal to the value of X attached to the variant of the Bulky (X) possessed by that Model.