Alexander's ever-expanding Tome of Knowledge

[mr.white]

I really like Arch devils. They can fly straight out of the box. They do pretty well in regular combat if you give them the usual protective gear like Robe of Shadows, luck item etc. But what makes them great is that they are tough units able to cast Flame Eruption and not die the next turn. That spell can really rack up the kills against regular units.

The research cost is high(Blood 6, Construction at least 4, Evocation 6) but not insane.

Haven't tried it in a serious game, but I think it's worth a shot.