Heroic: Lei Shi

Soloed last week and did not get this. I changed to 10 man the following week and got the achievement.

FWIW, I worked on all of the Terrace of Endless Spring heroic kill achievements (Heroic: Protectors of the Endless, Heroic: Tsulong, Heroic: Lei Shi, and Heroic: Sha of Fear) for several weeks before I finally managed to get them all on a single trip. I had been changing up my raid settings each time, first trying on Mythic, then Heroic-10, and when I finally managed to get the achievements, I went in with raid set to Heroic-25, and I made sure not to single-shot any of the bosses. I also went through the conversation chain with the NPC just inside the entrance before engaging any mobs (I hadn't done that prior to engaging any mobs before), but I have no idea whether that contributed to my finally getting the achievements.

Hope this helps someone.