Posts from RTF is a global modification that replaces all towns in the game.

Ideally, such a war machine should differ from a regular ballista not only in its accompanying units, color, and electrical or fire effects. It would also be good to give it at least a speed of 1.
In theory, artillery should be very effective in ranged combat and fall apart with a single hit in melee combat, and considering that it is a "large creature," the probability of it being disabled will be extremely high. Also, there shouldn't be too many of these units.
To avoid parallels with the ballista war machines, I would suggest designing such a unit as a cannon or mortar with an area-of-effect attack of 3x3, or simply give it a "crossfire attack."

Added 4 minutes later
As I wrote above, such a unit should not be numerous, which means its tier should be at least the fifth, and it should be made to match this level (some kind of hellish machine sweeping everything in its path).

Nothing prevents making a tier 4 unit with a low stat increase.
The problem with the ballista is that it can't move at all; there's no animation. If there were an animation, I would have to abandon the idea of gnomes because I can't synchronize their movement with the ballista's movement.

I don't want to make a mortar; it's not in the style of Ashan :D. But one of the upgrades could have a close-range flamethrower (like Greek fire), and for long-range, something else, like a magical stone that shoots darkness or fire.

In my opinion, creatures shouldn't become completely different after an upgrade. A ballista turning into a flamethrower is a bit much. Although, who knows what dwarves are capable of.

There's nothing stopping us from making a fourth tier with a low stat increase.

The problem with the ballista is that it can't move at all; there's no animation. And if there were an animation, we'd have to abandon the dwarves because I can't synchronize their movement with the ballista's movement.

I don't want to make a mortar; it's not in the style of Ashan:D

nothing prevents making a fourth-tier unit with a low stat increase.
The problem with the ballista is that it can't move at all; there's no animation, and if there were, I'd have to abandon the dwarves because I can't synchronize their movement with the ballista's movement.

I don't want to make a mortar; it's not in the style of AsKhan:D, but one of the upgrades could have a close-range flamethrower (like Greek fire), and for long-range, something else, like a magical stone that shoots darkness or fire.

In my opinion, creatures shouldn't become completely different after an upgrade. A ballista turning into a flamethrower is a bit much. Although, who knows what those dwarves are up to.

It looks clunky.
And can't you make it move without animation? - I don't know exactly how it works, but why does it need animation to move? - at most, the non-rotating wheels will be noticeable.

The ballista on the fourth tier looks pathetic. It should be a higher tier. On the sixth, by the way, there are no archers at all, so it will look good there.

There's nothing stopping me from making a Tier 4 unit with a low stat increase.
The problem with the ballista is that it can't move at all; there's no animation for it. If there were an animation, I'd have to abandon the idea of Dwarves because I can't synchronize their movement with the ballista's movement.

I don't want to make a mortar; that's not in the style of Ashan:D. But I could give one of the upgrades a close-range flamethrower-like weapon (like Greek fire), and something else for long-range, like a magical stone that shoots darkness or fire.

How about making the ballista magical, placing an adept and a dwarf on it, and having the adept simply teleport the entire structure a few squares. Not across the entire field, as that would be too powerful, but say, 4 squares. This could be explained in the lore by saying that the ballista is huge and difficult for a mage of that level to teleport, while a hero could move it wherever they want using a spell.

Added 2 minutes later
To clarify: I mean making the movement with a teleport animation.

how about making the ballista magical, placing an adept and a dwarf, and the adept simply teleports the entire structure a few squares. Not across the entire field, as that would be too powerful, but say, 4 squares. This could be explained in the lore by saying that the ballista is huge and difficult for a mage of that level to teleport, while a hero could move it as and where he pleases using a spell.

Added 2 minutes later
to clarify: I mean making the movement with a teleport animation.