https://www.trueachievements.com/GroatHardstroke.htm 's idea in the comments of
Br0ken Ghost 's solution was so good, I had to make its own video so everyone could be aware.
The fastest way to unlock this achievement involves creating a custom castle, with only a single bonus room structure, right next to your gate. Kill an enemy at the beginning of the round and then proceed to blow up your gate, if you're explosive is levelled it should demo your structure as well, thus ending the level and posting you to the leaderboard.
Rinse and repeat for all 16 survival levels and you're 30g richer