Since PhilD's challenge was quite enjoyable (win against AI dwarves on Trinity Isles using any one type of undead unit), I thought I'd come up with one of my own:
Win any scenario vs the AI using only Plaguebearers (the Afflicted unit). You can choose the map and the AI race. Have fun
Only 3 cities of your race, but that doesn't matter as your recruitment limit is mostly gold. Gold mine on the way to the fight helps, too, plus Dwarves don't have healers, and their cities have only 18 Influence.
But that was a fun one. Plaguebearer is probably my least loved unit