Peter let out a breath, and nodded. "I've been hurt before. I've been in pain. And I've gone through more than a few ways that people couldn't imagine were physically possible, let alone survivable." His voice quieted a moment. "Claire's ability... our ability. She's likely told you by now, but it's as much a curse as it is a gift. Maybe more, in the right hands. I'm not going to lie and say I'll be ready for anything, but... I at least have some precedent for that. I can take it long enough to try to fight back."
He listened to Dean patiently, attentively, not just hearing the words, but taking them and assessing them. Peter ran a hand through his hair and shut his eyes. "So it's not just a matter of finding out what can hurt him, but what can weaken him enough to let the other things take effect. I doubt I'll be able to kill him, but my powers aren't mystical or divine. They're just... physical. There. If he's never encountered something like me before, it might be an advantage."
The next part was the hard one to explain. "I've suppressed most of my powers. I absorb them just from being near someone with an ability, but six years is a long time to be picking things up like that. I don't want to be all-powerful." He wrung his hands, looking at the floor away from the young man. "When it first manifested, absorbing too many powers would knock me into a coma. Even with Claire's ability, opening up all of them at once might kill me. If I have two or three days, I can unlock them slowly enough to survive the process."
Then he lifted his eyes, looking seriously at the hunter. "Do we have two or three days?" Peter's eyes told the story. There was a risk. A definate risk. But right now, this was the only option they could find. If it was a chance to kill the bastard, it was worth the risks. And Peter would rather die with a plan, than wait to be cut down unprepared.