The hotkey tied to keyboard (i also used #2) worked wonderfully.....as I single pumpkin each one poofed when the hotkey was hit, advancing to the next pumpkin and they disappeared just as fast as I could hit the the key.
I tried the stack splitting but always came up a few seconds short. Here is how I did it:
Collect 20 pumpkins. Spread them out individually in a bag (20 singles). Make a hot key for the pumpkin (hold down cursor on a pumpkin until you get the hotkey). Move hotkey to a bar (I used my #2 key). Move into chamber, and then start hitting #2.
You can obtain this achievement using only one player. (Multiple players will just need to coordinate.) 1. Loot 20 pumpkins from pepponites. 2. Split the pumpkins into 2 stacks of 10. (suggestion: leave inventory bags open for now.) 3. Enter the small tower between Barkley and Ghrelchla. **15 second timer starts as soon as you enter.** 4. Right-click a pumpkin in one stack, then immediately right-click a pumpkin in the other stack, repeating as quickly as possible. (Note that the 1 second recast timer on pumpkins is **per stack** not per pumpkin.) 5. Complete the Mashing Pumpkins mission. The Black Thumb achievement is awarded on completion of the mission.
Addendum: Although I received a confirmation message in the chat window saying I obtained this achievement, the achievement itself on the /ach window under HoT --> Conquest will not update even after 2 additional attempts. Submitted as a /bug. --Vinny