Once, long ago, I was playing on a Gold single player scenario. I don't remember its name, but I started out in an imperial city in the central part of a large mountain spiral. Having my starting commander decently leveled, I got slightly bored after a dozen or so turns.
Then I hired an archangel and gave her a strong mercenary, IIRC an orc chieftain or something similar. Another dozen or so turns later (whee - creative use of haste spell), I have an archangel commanding three units and basically destroying everything coming near her.
Especially those "omg wand unit kill" AI heroes. That was so satisfying :)
What are your stories?

Well I don't figure that this is an amazing achievement or anything, but instead of converting 60% of the land in the Empire's final saga mission, I beat it by storming the legions' capitol and beating the guardian. I had my leader holding 2 banners of resistance (+20% armor apiece for 40%), and bought the dwarves' armor spell from a merchant on the east edge of the legions' portion of the map. Casting that with Holy Armor brought my entire party's armor to 90% which translated into only 20-some damage per hit from the guardian, which my healer mopped up each round.
The hard part was sneaking my way to the capitol without getting nuked with a Sinestra Ignis spell that would kill off my support units. I used a staff on invisibility that I had stumbled upon. The Empire has a much bigger disadvantage than you might think with its lack of stealth spells.