After some time I again managed to play around with the code and finish some other boats and heroes.
1. Biome variants: some trees typical for winter environment provide an "aura", which tells units to use specific visual variants - who would walk in sandals on snow?
2. Another minor update concerns monoxyla: melee units help with rowing, making the boat faster, while ranged units slow it down, but they can fire from the board.
3. Hunters (basic archers) can now swim; while swimming, ranged units can use only melee attacks.
4. Ponies! Cavalry units use smaller horses - only elite riders switch to high ones. I guess this is more historical for the setting. Not that it matters much, but maybe you would like to use the animations.