Siege Weapons

[Arkhios]

I had an idea of adding piracy elements to a campaign of standard fantasy, and I came to think of the artillery pirates usually might have on their ships. Here are a few, and I could use some help with transcribing them so that they would make sense with minimal effort and be mostly in line with the rest of the language in 5th edition.

Ballista:
Size: Large
Actions: 3 actions to prepare the shot, 1 action to aim, 1 action to fire.
Area of effect: 5 ft x 200 ft. line
Damage: 8d6 (average 28) piercing damage (Dex save to avoid)
Siege Weapon Drawback: ?

Cannon:
Size: Large or Medium?
Actions: 3 actions to prepare the shot, 1 action to aim, 1 action to fire.
Area of effect: 5 ft x 200 ft. line
Damage: 14d6 (average 49) bludgeoning damage (Dex save to avoid)
Siege Weapon Drawback: A cannon has a strong recoil, and anyone directly 5 feet behind the cannon at the time of firing must make a Dexterity saving throw or take 4d6 bludgeoning damage and be knocked prone.

Catapult:
Size: Huge
Actions: 4 actions to prepare the shot, 2 actions to aim, 1 action to fire.
Area of Effect: A point of your choice within 200 ft. range
Catapult Missile:
Single: 10d6 (average 35) bludgeoning damage in a 20 ft. radius sphere (Dex save half)
Mortar: 14d4 (average 35) bludgeoning damage in a 30 ft. radius sphere (Dex save half)
Siege Weapon Drawback: Catapult is inaccurate weapon and the chosen point of origin has a margin of error of 3d10 feet minus your intelligence modifier (rounded down, minimum 0) in random direction.

Trebuchet:
Size: Huge
Actions: 6 actions to prepare the shot, 2 actions to aim, 1 action to fire.
Area of Effect: A point of your choice within 300 ft. range
Trebuchet Missile:
Single: 14d6 (average 49) bludgeoning damage in a 20 ft. radius sphere (Dex save half)
Mortar: 20d4 (average 50) bludgeoning damage in a 30 ft. radius sphere (Dex save half)
Siege Weapon Drawback: A trebuchet is inaccurate weapon and the chosen point of origin has a margin of error of 2d10 feet minus your intelligence modifier (rounded down, minimum 0) in random direction.

When attacking with a Siege Weapon against a very large target, such as a ship or a creature of at least huge size, you make an attack roll against it with a bonus equal to your Proficiency Bonus + your Intelligence modifier. You make the attack roll only once, and compare the result against all valid targets within the area of one missile.
All other targets within the same area are subject to a saving throw DC equal to 8 + Proficiency Bonus + your Intelligence modifier. If the saving throw fails, the targets are affected by the missile as normal.

[Flashy]

So if a cannon has a 5 man crew or a trebuchet had a 9 man crew you can fire them once a round? Is that intentional?

[Arkhios]

So if a cannon has a 5 man crew or a trebuchet had a 9 man crew you can fire them once a round? Is that intentional?

More or less, yes. I mean, it does make some sense with a cannon, but it might not with a trebuchet. It could have a minimum rounds required to fire a trebuchet, if people think that's better.

[khadgar567]

No toys to launch annoying wizards in to castle walls

[Bharaeth]

This is good stuff. Some thoughts of mine:

* rolling multiple d4s for damage feels unpleasant; maybe it's just me, and I rarely have as many d4s as I do d6s, but a bunch of d6s is somewhat easier to eyeball the result of than d4s. Maybe convert the damage to d6s, instead, to be a bit more user-friendly

* With the ballista and cannon, I would be tempted to have the damage be reduced by the number of targets it chews through, to eventually slow it down - maybe only dealing leftover damage to the extra targets, after the first one is reduced to 0 hp. Especially with ballistas. Or maybe, reduce the damage by the smallest 1d6 worth after each target? I know that mechanic doesn't exist much in 5e, but it kinda works: so, if you roll 8d6 for the ballista, and results of 1, 2, 3, 3, 4, 4, 4, and 5, we're looking at 26 damage. Hits one guy, then you remove the 1, so second takes 25 damage; then remove the 2, third guy takes 23 damage, and so on. Also, the ballista should probably do a knock prone, too

* ballista drawback should probably be recoil, too, as even basic crossbows have recoil of some kind. Maybe just 1d6 damage and prone?

* part of me wants to suggest that the margin of error for trebuchets and catapults should be reduced by Int score, not mod - because what difference would -2 or -3 feet make? Perhaps, as d&d uses increments of 5 feet, swap the 2d10 feet for 1d6 (-Int mod) x5, and the 3d10 feet for 2d6 (-Int mod) x5

* and something else that comes to mind: the non large targets should probably have advantage on their Dex saves to avoid, if they're not locked in formation, that is, with the space to move around; although, not sure if that should apply to the ballista, which I guess is more anti-personnel...

[King539]

There are already siege engines in the DMG...

[Arkhios]

There are already siege engines in the DMG...

And they are illogical. A cannon should hit multiple targets in a line of effect, for example. Or would you say that a cannon ball, that can pierce the hull of a naval ship and potentially sink one, would stop after it's first hit on a person? I seriously doubt it. Also, their attack bonuses are very arbitrary. Where do they come from? Shouldn't the one who's aiming and shooting with one be able to affect the outcome in any way? A cannon at the hands of an inexperienced rookie is far less effective than at the hands of a artillery veteran.