Here are the last set of rules from Grey Knights vs Eldar two weekends ago.
JJ typing, Shooting with Walkers 40k6 pg 84
When firing a Walker's weapons, pivot the Walker on the spot so that its guns are aimed at the target (assume that weapons mountd on a Walker can swivel horizontally and vertically up to 45 degrees[sic]).
Context: Was shooting Psyflement at Fire Dragons. Thought they were like infantry that it really doesn't matter which way they are pointing (Turning and Facing 40k6 pg 10). Not the case with Walkers. My bad.
Jink 40k6 pg 38
A model with this special rule that has moved in its Movement phase gains a 5+ cover save until the start of its next Movement phase.
Context: Shawn wanted to confirm that he just has to move the Fire Prism to take advantage of Jink. Not that he had to move a certain number of inches. Informed yes. He proceeded to move the tank only an inch at a time each movement phase. Damn solid tactic in my opinion.
Night Fighting 40k6 pg 124
If the Night Fighting rules did not take effect during game turn 1, roll a D6 at start of Game Turn 5, on a roll of 4+, the Night Fighting rules are used for the rest of the game. On a roll of 3 or less, you must roll again at the start of every subsequent game turn - as soon as a roll of 4+, is rolled, the Night Fighting rules come into play for the rest of the game.
Context: Forgot to roll Night Fighting in first turn. Rolled in turn five and did not roll 4+. Shawn wanted to know if we roll again in turn 6. Wasn't sure myself. Yes you do.
Denial Units 40k6 pg 123 first bullet point
Denial units are those squads that can prevent an enemy from controlling an objective. In Eternal War missions, all units (including troops) are denial units, save for the few exceptions given below.
*If is a vehicle, or is a unit currently embarked on a transport vehicle, or is occupying a builiding.
Context: I thought a Psyflemen assaulting Dire Avengers on an objective for the last two turns could deny them the objective turns out it does not.