Sir Galveston - all Elementals
I remember this fight like I did it yesterday (even though I did it back in September) because it was quite difficult. I managed with the Electrified Razortooth, Pandaren Water Spirit, and, a Living Sandling (against Greatest Foe). The Living Sandling is a rarer pet but it's not that hard to get these days. You can get it from Throne of Thunder, the trash after Horridon (if I recall correctly). However, I do think there was a lot of luck involved, and a Living Sandling is probably not the ultimate answer. It's just what I won the fight with (and maybe that was pure RNG?).