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Instead of new machines or improvements to old ones, you could introduce a loader, a medic, an armorer, and an engineer into the game, in addition to the machines, corresponding to the ballista, the tent, the cart, and the catapult (as well as the Towers). They could be hired either in the forge or in special buildings. Each Faction has its own appearance for these specialists. You can have either one or several specialists at a time. All four have their own separate turn, defense, health, initiative of 10, and special skills, and also allow the hero to control machines of their type if he is not able to do so due to a lack of the necessary skills (except for the cart).
Loader:
-Give the ballista +X to initiative for the next few turns.
-Kill one creature in one friendly stack and "charge" it into the ballista. At the same time, the next shot of the ballista will deal X more damage (where X is the amount of health of the "charged" creature) and will have features depending on the creature (if you charge an assassin, the shot will poison the target, etc.).
Medic:
-If the hero's tent cannot resurrect creatures, it gives it this ability (permanently while the medic is alive).
-Give the tent +X to initiative for the next few turns.
-Kill several creatures in one friendly stack for X health units, while resurrecting X health units in another friendly stack (X depends on the hero's level and his corresponding skills and abilities).
Armorer:
-Like the hero, attack any enemy stack on the battlefield, with a strength twice as low as the hero would attack with.
-Move a friendly stack capable of shooting closer on the line (scale).
Engineer:
-Give the catapult an additional shot for the next turn with a separate target.
-Weaken the next shot of the catapult by X times, while injuring all creatures standing within a radius of Y cells from the wall into which the catapult fired, with the strength of the chosen Chaos magic spell in the hero's spellbook, while taking the necessary number of spell points from him.
-Enchant the next shot of one of the Towers with a chosen Dark magic spell, taking the necessary number of spell points from the hero.
-Give all Towers +X% damage to the next shot.