This achieve sucks. I hate it with all the fury of a thousand blazing suns.
Last winter a year ago, when MoP was ripe with age and SoO was already 5-6 months old, I spent all day, every day, camping in that stupid cave-in cave. I would work on my other machine and just kill Spelurk every 45 minutes or so when the cave-in spawned.
According to my Rarity add-on, I have killed Spelurk 387 times.
I still do not have that stupid talisman he supposedly drops.
All I have remaining for this achievement are the pets now. Wish I begged for the crab pet when it dropped back when it was all trade-able. Regretted it ever since taking on that achievement.
I could care less about the Bigger Bag achievement but I'm a Toy collector. I'm really not looking forward to getting the Toys associated with these rares.