That catches up with him in New Mutants #60.

That catches up with him in New Mutants #60. On the Ani-Mator's island, Doug steps in front of a shot meant for Rahne and is killed. It's a gunshot. After alien threats, magic and everything else this team has survived, that's what kills him. He doesn't suddenly discover another power. He sees his friend in danger and moves. The aftermath makes it worse. Rahne keeps trying to work out how she could have saved him. Warlock can't understand why giving Doug energy won't bring him back. His parents have lost their son, and the adults have to explain a death that never should have been part of sending him to school. Doug doesn't get the long run that most of these characters have had by this point. But he matters to the team well beyond the number of issues he's in. He helped them understand things they couldn't understand, helped save them from threats they couldn't overpower, and died trying to protect one of them.