I would rather leave the creativity part to Destiny but, I think they should make a gun that doesn't do damage in pve or PvP but, if you shoot a teammates ghost after he died, it would revive them. The shooting style would have to be a scout rifle or sniper. In my opinion, a scout rifle would be better since there's not that many exotic scouts. Also, it would be able to revive the taken teammate, regardless of what game type you're playing.