"A general rule of thumb, my friend, if it doesn't die when you cut its head off you have a very big problem." Hawke was very familiar with the various ways to kill strange things. He had even killed a varterral, a beast that actually came back to life later and he had to kill it again. These things were nasty and brutish but not the worst thing he had ever killed. The truly magnificent high dragon had been a very hard won battle.
Guns did not exist in Hawke's world. He was not familiar with firearms even though he had been here for some time had seen them. Hawke had no real understanding of how they worked or why. When Ken put the gun to his head Hawke was not expecting a giant golem to appear above the boy. This was certainly some sort of magic, like Ken had summoned a demon or spirit or something.
There were so many questions he wanted to ask but clearly now was not the time. Hawke assumed that Ken was vulnerable like this. He certainly wasn't fighting like he was before so he put himself into the role of protector.
"I can gather them in one place if you can hit them with enough lightning to stun them!" Hawke began to gather his magic, drawing into the well of mana that he had saved. "Once they're stunned I can behead them but only if you can knock them out for me!"
Enough lightning would stun anything. Anders had been a master of it, leaving raiders and darkspawn alike twitching as lightning coursed through their bodies. It was so easy to kill when your enemy couldn't fight back.