When using Advanced Targeting Computer (ATC) with a TIE Advanced, am I right in presuming that this is a normal "modify roll" activity and I declare that I'm using it in step 3 of the Attack phase? Or do I need to declare it during my roll in step 2?

When attacking with your primary weapon, if you have a target lock on the defender, you may add 1 [KABOOM] result to your roll. If you do, you cannot spend target locks during this attack.

I'm a bit confused because in the Rules Reference, it says you add any extra attack dice to roll during the "2. Roll Attack Dice" step, but modify using card abilities during "3. Modify Attack Dice". The wording on the card kind of suggests to me that it's during step 2, since it tells me not to use TL during the attack which would be in 3. Or is adding a [KABOOM] result to the roll happening at the end of 2, so that the defender gets to modify it in 3? If I don't add it until I Modify my attack dice, that would mean the defender doesn't have a chance to counter it.

Or am I just over-thinking this and it's obviously in step 2?

You're not adding a die to the roll, which would be in step two, you're adding a die result to the results of the roll, which happens in step three.

You're not adding a die to the roll, which would be in step two, you're adding a die result to the results of the roll, which happens in step three.

Yup. Adding die results is now firmly established as a dice modification, and unless there's an explicit timing instruction, dice modification happens in Step 3.

You're not adding a die to the roll, which would be in step two, you're adding a die result to the results of the roll, which happens in step three.

Yup. Adding die results is now firmly established as a dice modification, and unless there's an explicit timing instruction, dice modification happens in Step 3.

Adding results was always pretty firm - Add/Reroll/Change have been the three possible modifications from the beginning. "Cancel" is the only one that has been (and still is) in limbo.

But historical asides aside, the above posters are correct - it goes off as part of the normal modify dice results step.

Adding extra dice in step 2 is about making sure you're taking range bonuses and the like into account: i.e. adding actual, physical dice.

You're not adding a die to the roll, which would be in step two, you're adding a die result to the results of the roll, which happens in step three.

Yup. Adding die results is now firmly established as a dice modification, and unless there's an explicit timing instruction, dice modification happens in Step 3.

Adding results was always pretty firm - Add/Reroll/Change have been the three possible modifications from the beginning. "Cancel" is the only one that has been (and still is) in limbo.

But historical asides aside, the above posters are correct - it goes off as part of the normal modify dice results step.

Ok, so with all that in mind here is a situation. ATC equipped Vader shoots at an enemy with Elusiveness. Does the added die from ATC appear before or after the defender has a chance to force a reroll of that added Kaboom? I believe that the defender can not force the reroll of the added KaBoom since it does not appear until after he has his modify chances. If I am wrong what rule am I missing?

You're correct. After the attacker rolls, the defender applies any modifications before the attacker applies their own modifications. If the defender hasn't already used Elusiveness by the time the extra die is added by ATC, then they've missed their window to use the reroll at all.

Adding extra dice in step 2 is about making sure you're taking range bonuses and the like into account: i.e. adding actual, physical dice.

The real difference is that Step 2 is only about changes to the number of dice you roll in the first place. All effects that change how many dice you roll have to be used before the roll. If you have something optional, like Opportunist, you can't roll your normal dice first and then decide whether or not to get the extra.

Adding extra dice in step 2 is about making sure you're taking range bonuses and the like into account: i.e. adding actual, physical dice.

That's not quite true. The current rule on adding extra results is that the new result is an additional real die added to the current roll, and is modifiable in all the same ways. (TFA Rules Ref. p. 13)

The real difference is that Step 2 is only about changes to the number of dice you roll in the first place. All effects that change how many dice you roll have to be used before the roll. If you have something optional, like Opportunist, you can't roll your normal dice first and then decide whether or not to get the extra.

ObiWonka's not talking about results, he's talking about actual physical dice being added in preparation for the roll.

But you last comment is quite right. You can't add dice via abilities after the roll.

ObiWonka's not talking about results, he's talking about actual physical dice being added in preparation for the roll.

ObiWonka's not talking about results, he's talking about actual physical dice being added in preparation for the roll.

Due to rules changes in the new core set, adding results is also adding "actual physical dice" now.

I'm aware of that, but ObiWonka's comment was regarding Step 2 and in that step your only concern is establishing the correct number of dice that need to be rolled. There's no results at this stage because you haven't rolled anything.