siege engines on mounts

[LostDeviljho]

so a friend of mine recently came up with an interesting character concept. he would be a druid with a dire tortoise animal companion (with the warbeast template) and a ballista mounted on the tortoise.

however i'm not totally clear if that would be possible. as there doesn't seem to be any material directly addressing this. is there a way to put a ballista or some other kind of heavy artillery on a mount?

[Sir Chuckles]

As far as I know, there is no ruling on proper location for a siege engine beyond it's size category. So if the creature was both large enough and strong enough to lift whatever it is you're mounting onto it, I'd say go for it. Elephants were sometimes mounted with small cannons.

I'd probably make them have "Mobile Weapon Platform" be a learned trick via Handle Animal, and possibly, depending on the animal, impose a small penalty to aim.

[Flashy]

As a DM who usually tries to be pretty careful about interpretation of the rules there is nothing about this idea I don't love. As far as I know nothing in RAW prevents it at all.

I agree with Sir Chuckles: make it a specific trick that has to be taught, maybe make the druid take a proficiency to fire the ballista properly and call it an awesome, awesome day. Among other things it's not like it's more OP than what a druid high enough level to have a dire tortoise animal companion could do anyway.

[Bullet06320]

real life examples include elephants mounted with cannons, and camels with machine guns
love the idea, I just haven't come across any rules to help
but applying a negative to hit while moving would be appropriate