Ideas and suggestions.

With diplomacy, you can implement a mechanic where units join you, similar to how Necromancy works, with 5, 10, or 15% of the enemy units joining your side.

Instead of 15 skeletons joining, 15 Cyclops or Ducks would join (and no one would stop you from converting them into skeletons if they don't fit in the stack, as there's an external converter available). A very balanced change.