MArcomage

This may seem really cheap for how much damage it can unleash, but bare in mine, you opponent would always know your hand, and it is only effective if he/she plays a big attack first.

This works more as a deter ant card, preventing your opponent from attacking you until they can effectively play their attack card without having their recruits significantly lower than yours.

The problem is what is "attack last round"? We can only detect if your wall or tower was damaged by the opponent (and the amount). But we can't tell if it was done by attack card (without searching card history).

Also the damage can be done by multiple cards for example Wind + Invisible squad. In this case no attack card was used but wall and tower was damaged. Should this card also cover such cases?

Yes. It's still 'damage'. The card now reflects that.