Hey Victor ^^. Shposhae is a great location, however, I would watch out for the "wisp" type enemies. Some of those enemies, especially the ones that linger around the large seashells, only "disappear" and are not actually "defeated". Since there isn't a counter and I didn't earn my achievement this way I can't confirm they aren't counted, but I have a suspicion that they will not due to the verbiage. You can always test this theory by bringing a mule down and killing 100 wisps to see if that mule gets the achievement.