Ok, based on discussion, this is what has been changed so far with this card:
Shield Bash is a passive skill. It treats most shields equally.
Shields that cannot be targeted or destroyed are immune from the Shield Bash skill.
If Shield Bash is activated with a Bone Wall in place, then 2 bone walls are removed from the stack.
If Shield Bash destroys a shield, then flail does its normal attack damage to the enemy and the weapon is delayed 1 turn.
Keep in mind that the poll is running, and this card will certainly undergo more changes. I set the poll to end in 10 days, but really just playing by ear.
And, if there're bigger problems with this card that aren't represented in the poll, don't worry: I am certain they will be revealed through discussion and further refinement of this card.
Be sure to go over the changes stated above, or in the card notes, before voting!
Edit: Grammar