(WB2)
Tell me some of the secrets you have found in the game so we can all help each other! For example on secret is walking into a ring of mushrooms sometimes spawns troops, or that an infernal tower is much better when leading the daemons

There are a few map-specific 'secrets' along the same lines.

There's a map where your troops will heal a small amount when walking near the 'waters' - it's alluded to in the map's description before you play it.

There's another map with a large mountain in the centre, which provides a reward to a hero reaching the top; again this is hinted at in the region's description.

Along the same lines as the infernal tower with the Daemons, dwarf builders (Smiths) count as 2 troops when working in mines, although I think that's also a loading screen hint so probably not so 'secret' :).