Your opener dictates where your burst begins, along with where your No Mercy will come up relative to the fight. As such, some fights will require earlier (or even Prepull NM) to optimize more or to gain usages of Blasting Zone or Gnashing Fang (P3S). However when in doubt you can follow the 1-2-3-NM! Opener until you encounter a fight requiring an alternate approach
As content is released, various openers may be utilized from fight to fight for all manner of reasons. Learning only one opener can restrict you if you plan to do all forms of content.
1-2-3 No Mercy!
Our Standard opener. Allows us to line No Mercy into opening raid buffs while keeping our ammo straightforward and simple with adequate timing for our strength potion.
If the timing of a fight requires Gnashing Fang/Blasting Zone and/or No Mercy to be used earlier for line up, Keen Mercy opener pushes GF ahead two GCDs to secure earlier uses through the fight. This is done on a fight by fight basis and depends when bosses will be leaving the battlefield, and is only worth using if it secures an extra use before downtime occurs. (P3S at 2.43+ being an example where an earlier opener can allow you to maintain a full GF combo on the boss before it leaves for Add Phase).
Lightning Shot Opener
If you are required to pull a boss and center it, and want to do so quickly and efficiently you can open with Lightning Shot. However, here we do No Mercy after Brutal shell to keep Gnashing Fang still at third GCD to ensure it’s still lined up to where it is in the original opener. An example of when to do this without fight specific positioning requirements would be if your Ninja wants to pull into a precast Doton – but due to the slight loss versus the 1-2-3-NM! opener, ask if your cotank can pull with a ranged attack for a smaller loss.