Disguise builder troop

A troop that looks like a builder and if you place him at the beginning of the game he won't be attacked until he attacks but if you place him after the base has already been alerted then he will be attacked. He jumps walls like normal builders and he attacks defenses and you can only place 2 or 3 until the base is alerted and they will be attacked. I kinda think that they should be immune to traps but as that is somewhat unfair I'm open to whatever. I don't know if they should be melee troops or more like the skeletons and place a bomb that also kills them, if they place a bomb though it negates the not being attacked until attacking part. Some people might find this troop unfair so if you have any suggestions let me know and if it doesn't get added into the game it won't bother me a whole lot.