I don't see the point in this, but it can be done if you really want to:D
You need:
2 Explosion
No, but why do you need Explosion? How many Archons will you take down with it, even with 99 Magic Power?
3 Protective Field
4 Sphere of the Muddy Lake
Why do you need Protective Field, why do you need Sphere? Everything can be solved perfectly without it...
6 99 Power and Knowledge. Just for fun, you can double the mana in the dungeon.
And what's the point of this one? You might even offend him, but it's just stupid.
7 Sandglass, to bring the morale of the Archangels down to zero.
Sandglass NEVER affects morale!!! You're wrong.
By tactically moving the Imps to the corner, we set up a Power Field (it's a pity it doesn't last long, I'm not sure how long. It's important to know how long. It's easy to find out. We blind the Archangels and wait for the field to disappear). We set up the field again. We attack the Archangels with Explosion, dealing more than 11500 damage, waiting for the turn after which the field will disappear. In this turn, instead of Explosion, we blind the Archangels. Then we set up the disappeared field AND keep attacking until the final victory.
Don't worry about mana, 4000 will be more than enough.
Tactics are not necessary at all!
Power Field ALWAYS lasts for two turns.
In general, this task can be solved much easier by summoning elements - it's simpler and easier ;)