The main setting of the story, Polnya seems to control a fair amount of territory besides the valley that contains The Wood. It has a significant border with its rival Rosya, which also borders on The Wood. (In fact, as the story goes on, it becomes apparent that the Wood is stoking the rivalry between the two nations for its own purposes.) The two countries have a bit more of an Eastern European flair than your typical fairy-tale fantasy countries. As the name suggests, Polnya seems based on Poland - it even has an monarch that seems to be elected (or at least acclaimed) by the 'Magnati' nobility, where as Rosya is presumably Russian. Cannons make an appearance, but I don't recall any references to personal firearms, so a 15th or 16th-century level of technology seems appropriate. A Polnyan army could include:
- A Hero General (Prince Marek) or a Knight General (if led by his more sensible brother Prince Sigmund)
- A Magician (one or more of the court wizards like the Dragon or the Falcon.)
- A Cleric (Either a priest with holy relics, or Agnieszka, whose magic seems to be notably different from that of the court wizards.)
- Artillery (Early cannon, but firing enchanted cannonballs.)
- Knights and/or Riders (Heavy or light Polish-style cavalry, though there's no mention of anything like the famous winged hussars.)
- Spears (Infantry armed with pikes.)
- Blades (Infantry armed with axes for venturing into the Wood.)
- Hordes (Peasants with torches and agricultural implements.)
The stronghold could either be the Dragon's mysterious tower on the edge of the Wood (remnant of an earlier Lost Age) or a Eastern European city wall and gate. A Rosyan army would probably be quite similar, though we learn very little about the personalities on the other side of the border.
The Wood had lain dormant in its valley for a very long time, ever since it destroyed a previous civilization, of which the Dragon's tower seems to be the last remnant. At some point, the ancestors of the Polnyans and Rosyans moved into the valley, and the Wood awoke again, its hatred for humanity as strong as ever. Fire and salt can hold it at bay, and powerful magic can drive it back for a little while, but the Wood is always growing, always encroaching on the settled lands. Weird creatures and strange, twisted animals live in the Wood, but the greatest threat is corruption - contact with any part of the Wood, even the drifting clouds of pollen, can turn a person into its tool. Forces of the Wood might include:
- A Magician General (The Wood-queen - a humanoid figure covered in bark and leaves.)
- Behemoths (Large magical creatures like chimeras or hydras.)
- Beasts (Corrupted animals such as wolves or cattle.)
- Warbands (Stick-like Walkers, who snatch the unwary and carry them into the Wood.)
- Knights or Blades (Giant silvery mantises that guard the heart-trees.)
- Hordes (Humans in an early stage of corruption.)
- Lurkers (Grasping tree branches, brambles, pit traps, sudden betrayals by fellow soldiers who have let their guard down - the Wood is full of dangers.)
- Any of the Polnyan elements, being used as pawns of the Wood.
The stronghold could be a heart-tree with silver bark and sickeningly sweet golden fruit, either deep in the Wood or planted in an abandoned village.
If you wanted to make the game more of a challenge for the Polnyans, you could also develop some scenario-specific rules. If the Wood is the defender, much of the table should be bad going - it is a forest, after all, and those Lurkers need somewhere to deploy. It might also be appropriate for the Wood not to have a General - the Wood-queen doesn't really show up in physical form until near the end of the story. And finally, it might be interesting to have the Wood take control of elements that are attacking it - either by letting it deploy Polnyan elements that were destroyed in combat, or perhaps (more insidiously) ones that merely came in contact with elements of the Wood's.
All in all, these armies would be much more feasible than some of my previous Hypothetical Hordes musings. There are plenty of historical figures who could be used for the Polnyans, and various animals and plant-creatures are available for the Wood. I'm almost tempted to see what I could podge together from what I have on hand already...