Let’s come up with new “war machines.”

You can leave all the machines as they are. Add upgrades for ballista and tents, depending on the faction. And slightly change the model during the upgrade. Here is my suggestion:
Inferno - Ballista: Essence Theft - When killing n creatures, there is a 40% chance that n:5 imps/devils/fiends will appear, i.e., 5 times less than the number killed. The percentage chance depends on the skill of opening the gates. Basic - 40%, developed - 60%, skilled - 80%, master - 100%.
Tent: Sinful Mana - There is a 40% chance that when resurrecting a dungeon demon/lord, it receives one one-time free dark spell of level 1-3.
When I say "resurrection," this does not mean that the unit must be completely dead.
Sylvan - Ballista: Entangling Bolt - There is a 60% chance that when hitting, the "Slow" spell will be cast, and there is a 30% chance that the unit will be "entangled." "Entanglement" does not affect large creatures.
Tent: Lucky Healing - When healing, there is a 25% chance that the unit's luck will be increased by 1 for one turn.
Necropolis: Ballista - Rotting Shot - There is a 40% chance that when hitting, the unit's morale will be reduced by -1. Does not affect undead.
Tent: Cultivation - When resurrecting creatures, an additional number of resurrected creatures is added; the number depends on the level of the unit and the number of units you are healing. Here's how it looks: level 1-3, 1 to 20; level 4-6, 1 to 10; level 7, 1 to 5. That is, the number of resurrected creatures appears in proportion to their level. In other words, I had 60 zombies, one was killed, I resurrected it, and received an additional +3 zombies.
Dungeon - Ballista: Treacherous Strike - the shot penetrates n% of the defense. The percentage depends on the attack skill. Basic - 20%, developed - 40%, skilled - 50%. Also, +5% for the "Attack" and "Shooting" skills. A maximum of 60%.
Tent: Hydra Blood - Once per battle, you can transfer the regeneration of a hydra/dungeon/chaos creature to another unit of the Dungeon faction. The regeneration parameters remain the same. Moreover, the hydra itself loses regeneration. To activate the ability, you need to click on the spellbook in the tent (it is implied that you need to have the "First Aid Tent" skill).
Academy - Ballista: Chaotic Charge - When hitting, there is a 60% chance that the "Magic Arrow" spell will be cast, a 30% chance for the "Lightning" spell, and a 10% chance for the "Chain Lightning" spell.
Tent: Obsidian Chamber - When healing obsidian gargoyles/obsidian golems, at least 3 creatures are resurrected.
Haven - Ballista: Punishing Aim - When hitting a creature, when the unit that was shot by the ballista attacks your unit, it deals only 70% damage; the remaining 30% is "taken back." When hitting another creature, the effect is removed from the previous one. The effect lasts until the end of the battle, until it hits another unit.
Tent: Holy Calm - You can "heal" an enemy unit, and with a 40% chance, the "Holy Word" spell will be cast on only it for the next turn. With skilled light magic, +10% chance.
Fortress - Ballista: Targeting - When hitting, there is a 20% chance that all archers of the Fortress faction will fire at the same unit that the ballista shot at. With the "Shooting" skill, the chance increases by 5%.
Tent: Rune Tent - When healing a unit, it may be given one free rune with a chance of n%, depending on the unit's level. Level 1-3, 50% chance of a level 1 rune; level 4-6, 40% chance of a level 1-2 rune; level 7, 30% chance of a level 1-3 rune.
Stronghold - Ballista: Roaring Bolt - When hitting, there is a 40% chance that the "Frighten" effect will be applied, and a 20% chance that the "Berserk" spell will be cast. Those with immunity to the listed effects will not be affected.
But this does not mean that if a unit is immune to "Frighten," it is protected from "Berserk"! And vice versa.
Tent: Blood Chamber - when resurrecting a creature from the Stronghold faction, there is a 40% chance that only the resurrected creature's rage will be increased by 0.4 of the number of points (that remain to be gained), as many as are required for the next level. That is, for example, I had 200 points (I'm saying this conditionally!), there are 1200 points in total for the next level. I have 1000 left to gain. I got a 40% chance. This does not mean that I get 400 points! (1000*0.4). This means that I get 480 points! (1200*0.4).
These are my ideas. If you promised to send them to Nival, do it! Otherwise, did I work for nothing? And yes, by the way, if the ballista has several shots at once, the effect is applied only to the first shot.
P.S. There is no need to say "nothing should be changed"! This topic was created to present your ideas and suggestions for improving/creating new combat machines! And not to express opinions about whether something should be changed.