Does it affect dodge? I do not think so. In fact the only thing that immediately leaps to mind is initiative. Any other big benefits of unnatural agility?

antony131073 said:

Yes it does. As with all Unnatural X characteristics whenever a test is taken based on such an characteristic (such as dodge) the difficulty is brought down by one stage for each multiplier [iH p. 226]. So with Unnatural Agility (x2) a Challenging (+0) dodge becomes ordinary (+10).

Khouri said:

The other significant benefit is Concealment and Silent Move tests. Being Agility-based skill tests, they benefit in the manner noted above, but additionally benefit as opposed tests - every time you make a Concealment or Silent Move test (which are opposed), you gain +2 degrees of success (a number equal to the modifier gained from Unnatural Agility) on any success, meaning that it's extremely hard to locate things like Lictors and Eldar Rangers (stealth specialists with Unnatural Agility - a stationary Eldar Ranger has a 100% chance of passing a Challenging Concealment test, and a normal Per 31 Guardsman has only a 0.1% chance in total of spotting the Ranger, increasing to 2.1% if the Guardsman has an Auspex).

antony131073 said:

Read the rules on Unnatural Stats in the Inquisitors Handbook p. 226.