Grand Strategy is this. Chooses D3 units before deployment. They must be infantry, jump infantry, monstrous creatures, or walkers. The ones chosen cannot be a unit with a independent character in it, nor can it be inquisitorial henchmen or ghost knights. Each unit chosen gets the following rules for the rest of the game.
Hammer of Righteousness
Re-roll to wound rolls of a 1 for the duration of the game.
Shield of Blades
The unit gets the counter attack special rule
Spear of Light
The unit gets the scouts special rule.
The unit can claim objectives as if it were troops.
OK. First the important part of this.......
First. This power is done before deployment. That is before combat squads are declared. (notice how this power just got cooler). Combat squads are done at deployment, so the powers they receive are now split up into your combat squads.
Second. They get scout. I don't know if this excites anyone, but I am drooling at all the possibilities. This alone makes me want to play a Grey Knight Army. I will btw, because Grand Strategy is just that cool. Do not forget that a unit with scout that is deployed inside their dedicated transport vehicle confers the scout ability to the vehicle. (pg 76 rule book if you need it).
Third. These units can now all claim objectives. (not the vehicles), however a walker under this rule could (edit: check comments, I probably misspoke on the walkers).
You get all of this for the very low price of a Grey Knight Grand Master, who comes in at 175. He gets other stuff as well, but that is for another time. Grand Master Mordrak also comes with this ability. Technically you could take two Grand Masters, giving you up to 6 units effected by the ability.
This ability dramatically changes how this army will operate. I want it, I will get it.