Yes, the cost is that you have to pick a particular effect to get the bonus; applying physical stress is kind of weaksauce, but Darclight's design is based around not having overwhelming power, but applying it really really well.  The 1d6 is also a slight cost, because of the probability of generating an opporunity.<br/><br/>Basically, he's good at kiling people with energy beams, knives, or punches to the throat, but not so much at technical fighting and finesse.