What is the timing window for playing Assassinate, Positioning Advantage?

What is the timing window to discard a card with Zillo to add a Block?

What is the timing window to cut Pierce by exhausting Zillo?

Go to the Rules Reference guise, page 5 to see the steps of an attack.

Assassinate/positioning advantage are modifiers that are played in step 4. Discarding a command card for a zillo block is also in step 4.

You’ll wait to exhaust zillo until step 7, after the opponent has spent the surge on pierce.

If an ability is "while attacking" or "while defending" and is removing or adding symbols or accuracy, it is played/resolved during step 4 (Apply Modifiers) in the order of timing conflict resolution. See https://www.boardgamegeek.com/thread/1631857/ability-resolution-order-during-attacks for an exhaustive list when and why's.

A1bert's exhaustive list on BGG is an incredible resource and document.

I've found that in a tournament, it's incredibly helpful to go step by step (being disciplined about it every time also avoids tipping your hand to your opponent about whether you're holding something like Tough Luck or Positioning Advantage ).

I usually keep in mind:

0: Before attack declarations

1a: Attacker declares attack and target
1b: Ask Defender if they have effects to play

2: Roll Dice Together

3a: Attacker re-rolls
3b: Ask if defender has re-rolls

4a: Attacker adds modifiers
4b: Ask if defender has modifiers

5: Attacker spends surges

6: Check Accuracy

7: Apply Damage

I'll "add modifiers to the topic," since it's resurfaced. Here are a few nuance issues that it's taken me time to appreciate, and if I'm off on any of these, please correct me!:

A: My current understanding is that each player gets only one "timing instance" per step: that is, after the attacker adds modifiers, the defender gets to add modifiers, but if the defender surprises the attacker here (say, with Parry to add a block), there's no extra chance to, say, use Hera's Call the Shots to add more damage in.

B: Each particular die can be re-rolled a maximum of once. So if an EQuay pirate forces the defender to re-roll a dodge on a white die, the defender cannot then use Cower to re-roll it again. Similarly, if you're attacking and the defender uses Guardian Stance to force you to re-roll your triple-hit red into a singleton, you cannot thereafter re-roll it with Professional to try for a better result.

C: (Here I'm most confused:) At my last Regionals in MN, the TO explained to one player that you can re-roll dice using separate effects within your own timing instance. That is, Ko-Tun could re-roll one die with Professional , then if the results were still unfavorable, re-roll a separate die with Officer's Training .

"C" is still subject to the mechanics in "A," and "B," so the attacker can re-roll with Professional , then separately with Officer's Training , but couldn't try to re-roll again after the defender re-rolled with Hard to Hit or something.

D: All dice re-rolled by a single effect must be re-rolled at the same time. So your Elite Sniper ERanger has to choose whether to re-roll 0, 1, or 2 with that ability at the same time; within a single ability , you can't re-roll them one by one.

C & D: You can only reroll each die once per attack. It's explicitly specified in the RRG. You can reroll a different die using another reroll ability after seeing the result of the first reroll. No-one can reroll the same die.