Is it possible to defeat 1000 Archangels with just one Imp?

You can blind them, and in the meantime, summon various creatures. And if there are more than one stack of Archangels (by the way, this isn't specified in the conditions – one stack or none, a minus to the author of the puzzle! :mad:), then you can use Berserk.
But in any case, you need to have a lot of skills specifically for this situation: either Ballistics, or Artillery, or Fire Magic... And it's impossible to do this just during the game.