I had this crazy idea... we have troops that can go over walls, troops that break through walls...but we haven't got this one yet (as far as I know anyway)...
This new troop could be a miner..with a bomb attached to its chest...and it digs under walls to give way to troops requiring one storage space (barbs&goblins)... but with each miner it only has a 1 tile splash damage so it makes a 3x3 square underneath the wall.. in order to get completely under you would have to send out 2 miners so that you have a space to jump in and out...but when a wall is at a high level it has greater foundations so it requires either more or higher level miners......
I have yet to think of a name for it yet &I haven't come up with stats yet but I'll post at a later date

