The drop rate on these stones is a little silly, I have power leveled 14 pets from 1-25 using only aquatic type enemies in the vale of eternal blossoms and have gotten one aquatic stone, I have spent at least 4 hours a day ( more on weekends when I am not working) farming cogblade raptors for the last 4 weeks and haven't seen a single mechanical stone from that. But the undead stones seem to drop like candy from the shadelings, I have been there three times, once to farm a rare shadeling for my collection, once just to try to farm a stone to use on my unborn Valk'yr, and once to show a couple of friends where to get the shadelings at. All three times I got an undead battle stone in less than 10 minutes after they started spawning. Still haven't gotten a mechanical stone from the trainers or from farming those stupid cogblade raptors. The whole reason I found this thread was googling in hopes of finding a better pet to farm since the cogblades seem to be few and far between when you are trying to kill 10,000 of them to get a battle stone to drop...guess it's back to blades edge mountains for me.