Just putting it out there, in case it isn't already common knowledge. If you want an easy win, or an easy loss if its used against you, check out a full stack of American long rifles in an early period game.
Invisible, longest range, skirmishing army.
The only counter is mass cav, and thats if you guess and predict it. Prepare to roll the dice and enjoy an extremely gamey, unfun, broken game.
ETW is in need of a balance patch big time. Between mortars and these early elite skirmishers, there is an issue.