Guild Wars 2

I decided to finish the missing achievements on the Gates of Maguuma Story, and I noticed that while doing Explosive Avoidance I had this achievement that was to keep hitting Aerin for the achievement “Sabotage Aerin” or the effect will disappear. thing is I went to do the Dashed Advantage, and came back since I was doing the Explosive Avoidance might was well finish but now I cannot get the Sabotage Aerin again since i done them all now, was it related to the Explosive Avoidance or it was an achievement by itself?

I’m sorry, can you keep it simple and say again which achievement – or whatever it is – that you’re trying to get?

I can only guess the one you’re talking about is the achievement Opportune Moment. In which case, allow me to refer you to a video guide, courtesy of Dulfy.net:

If you finished the chapter (and thus do not have the option to play that mission again), you must restart the entire chapter again (as far as I know). This is one of the major drawbacks to Anet’s current LS Story Journal system (and requiring you to play missions multiple times to earn achievements).

If I’m not understanding what you are asking, I apologize as it was a bit unclear.