Your Army

[Antiga]

The castle where you can get the dwarfen wife will gets new units/spells/items when taking her as a wife. Same for the elven castle where the elven wife is located. I'm guessing it counts for Zombie rina and the demoness as well. Finishing certain quests enables you to buy units from places where you were unable to buy anything before.

If you're still in the starter area's and let the furious paladin live, killing him will spawn a different unit set(undead) at his store.

[GreyBeard]

I have also noticed it is random, one time a merchant doesn't sell archers, few hours later he has hundreds.

I try to make notes of who sells what type of troop but since alot of it is random or the merchant runs out its not much of a help. Early game it helps since most merchants have a good stock of troops and items.

GB