This one seems pretty much tailor made for like Ensidia and paragon who do runs on their alts first. Still though it seems like they need to tone it down a bit, if someone DC's for some reason or something goes wrong that is outta control for the player then they cost 25 people an achievement they can never earn.
Call me crazy but, given past achievements similar to this one, I would venture to guess that it means on the current lockout, not on the very first pull. If that were the case, then they wouldn't have it on the meta achievement that's most likely tied to the mounts. That's just my guess, though. >.>
