Ideas and suggestions.

Cool ideas for spells: In the original King's Bounty (NWC, 1990), there were 2 field spells: Raise Control - increases leadership. In Heroes, you could make it so that it increases morale on your turn and the opponent's turn (if they attack) - it would be a fairly popular spell. Instant Army - increases one of the troop stacks by several units. In Heroes, you could create a function similar to the object I suggested:

1) Summoning Portal. Unlike the dungeon summoning portal, which for some reason clones troops instead of summoning them, the external Summoning Portal will allow you to buy troops from all available dwellings and cities. When visiting the object, a list of available cities appears (as when using the Town Portal spell), plus a list of external dwellings.