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

The enemy attacks. The demon runs to a corner and closes itself with a force field, and on the next turn, it attacks with an explosion. When the force field is active...

I think I misunderstood something. Where does it run if the archangels go first? They'll immediately take it down.
Also, various berserkers, etc., can only work in the case of a siege, and there must be either ballistics (if we are attacking) or artillery (if we are defending).