Probably more ideal in a siege situation where most spells don't really add anything to taking down a wall or getting loads of people over it

Quote from blakejohnson217 >>

"You're traveling through the underdark when a purple worm appears..." 

"A purple worm? We fought one of those in the last campaign; this'll be eas-"

"...With a canon."

 Some times I love reading the comments, almost as much as the article itself.
You, Sir, are awesome!

So if a Gargantuan creature with War Carriage can carry a Huge creature, can that Huge creature also have a War Carriage with a Large creature on it, and can that Large creature still have a Medium creature riding it and a Small creature on top of that?

I feel a pyramid of death war creature campaign coming on…

Quote from Jaeken >>

So...  In addition to MDC's point, I gotta ask: Where does the ammunition come from?  Especially for the ballista & trebuchet, how many shots are you planning to store on the beast's back?  Or is this a one & done attack?  Magically created ammunition?

To be fair, the ship vehicle rules don't really specify this either; I think it's safe to assume that the space occupied by the weapon also includes some nominal amount of spare ammunition, e.g- 10 bolts for a Ballista, and any additional ammunition requires you to sacrifice more space to accommodate it, or needs to be carried by whoever is operating the weapon.

The interesting one is the harpoon crossbow; 20 spare bolts seems perfectly reasonable, but to get the rope back you'd need to reel it in which should take at least a full action, assuming no target is currently harpooned, and if one is harpooned it should be more difficult (Strength checks, since the target has weight?). So for a short battle these probably are one and done, but you could always have multiple.

As for MDC's earlier remark about ground stability, I'm not sure if that would really be an issue? We're assuming a War Carriage platform on the back of a Huge or Gargantuan creature, so it should have the space for these weapons to be very firmly affixed. If I were DM'ing I'd maybe assume that the creature itself has to be stationary or gliding to fire a weapon accurately/safely, so can't be attacking itself in the same turn, otherwise maybe give a penalty to the attack roll and/or roll to see if the weapon is damaged and unusable as a result of a risky shot?

Loads of options, I think the key thing with vehicle and war monster rules is that they're a jumping off point to get you started, and really it partly comes down to whether the players or enemies are the ones operating these anyway (just handwave ammo if it's an enemy beastie the players need to take down).

So the harpoon crossbow is just about useless if the creature it’s mounted on can’t fly. You can counteract the dragging effect just by walking. If your walk speed is <30 than you can slowly, slowly be dragged in.

If the creature can fly, and the target can’t, then you could technically impale it and then just fly off. Doesn’t seem too useful otherwise.

The straps having their own stats seems a little unnecessary, but I like this overall! It reminds me a lot of the ogre howdah.

Am I the only one here who saw that a Gargantuan creature with a war carriage can carry four Large creatures and thought of a Gargantuan creature holding four Ogre Howdahs holding four Small creatures each? It's backpack-ception

Quote from HallaarKiirgalan >>

Am I the only one here who saw that a Gargantuan creature with a war carriage can carry four Large creatures and thought of a Gargantuan creature holding four Ogre Howdahs holding four Small creatures each? It's backpack-ception

 Each ogre and each of their passengers have crossbows (the small creatures have light crossbows, everyone else is heavy). The driver spot gets to operate a harpoon crossbow. They’re on the back of a storm giant with the enlarge/reduce spell. The giant also has a crossbow. They all take the ready action. You come within 60 feet and suddenly 22 bolts of various types impale you. Assuming they all hit and everyone has 10 Dexterity, that’s an average of 99 damage. And now you can’t leave.

Gonna use this to make me a frost giant Bard with a gnome-driven polka suit!

Quote from Haravikk >>

Quote from Jaeken >>

So...  In addition to MDC's point, I gotta ask: Where does the ammunition come from?  Especially for the ballista & trebuchet, how many shots are you planning to store on the beast's back?  Or is this a one & done attack?  Magically created ammunition?

To be fair, the ship vehicle rules don't really specify this either; I think it's safe to assume that the space occupied by the weapon also includes some nominal amount of spare ammunition, e.g- 10 bolts for a Ballista, and any additional ammunition requires you to sacrifice more space to accommodate it, or needs to be carried by whoever is operating the weapon.

The interesting one is the harpoon crossbow; 20 spare bolts seems perfectly reasonable, but to get the rope back you'd need to reel it in which should take at least a full action, assuming no target is currently harpooned, and if one is harpooned it should be more difficult (Strength checks, since the target has weight?). So for a short battle these probably are one and done, but you could always have multiple.

As for MDC's earlier remark about ground stability, I'm not sure if that would really be an issue? We're assuming a War Carriage platform on the back of a Huge or Gargantuan creature, so it should have the space for these weapons to be very firmly affixed. If I were DM'ing I'd maybe assume that the creature itself has to be stationary or gliding to fire a weapon accurately/safely, so can't be attacking itself in the same turn, otherwise maybe give a penalty to the attack roll and/or roll to see if the weapon is damaged and unusable as a result of a risky shot?

Loads of options, I think the key thing with vehicle and war monster rules is that they're a jumping off point to get you started, and really it partly comes down to whether the players or enemies are the ones operating these anyway (just handwave ammo if it's an enemy beastie the players need to take down).

 https://en.wikipedia.org/wiki/Trebuchet#:~:text=A trebuchet (French%3A%20tr%C3%A9buchet),manpower%20to%20swing%20the%20arm.

The above link is from wikipedia about Trebuchet, when posting I was thinking of a TV show documentary about building them and using tons of rock in the counter weight. 

Why do I think some basic things such as this is important? In general I know I do not know a lot of stuff and I have met people that do not know where hamburger comes from as well as not knowing how ducks reproduce and bear young.  So often now I try and provide more explanation when building things and not just say "PFM" or Pure Fracking Magic so as to help out those who may not have as good a grasp of things in areas I understand. 

Another area you touch on is solid ground to fire from which is very important with the forces involved.

You generally have the most issues when scaling up and down to a great extent, ie you put wheels on a small boat might be fine but putting wheels on the USS Iowa Battleship or a Super Tanker you have big problems, like wise you put wheels on an atom of hydrogen you have a very small big problem. So knowing where to draw the line is important.

Younger Me: I can say that in the past I have done things such as this when GMing and playing and at times it has been fine but other times it has lead to disruptions to the game. So now I try and identify areas in products that might cause problems in my game and move to change them before they can cause issues.

MDC

Imagine if someone used these templates for an Urban Arcana-style campaign. Look me in the eyes and try to tell me, with a straight face, that a red dragon with rocket pods and heavy machine guns strapped to it wouldn't be the most metal creature ever.

Quote from spammdc >>

Another area you touch on is solid ground to fire from which is very important with the forces involved.

Sure, and they shouldn't be ignored, but part of the issue I think with catapults on the ground is that there are limits to how well you can fix them to the ground; you could drive stakes into the ground directly, or use straps/ropes to do so at a distance (distributed over a larger area) but the force to hurl a boulder will eventually rip those from the ground. Piling weight on is simply easier. Catapults mounted on a tower of a castle though could use iron hoops embedded into the stonework, avoiding that problem.

Catapults (mangonels in particular) have been used historically on ships, and the advantage to firing them from a ship is that you can design a ship's deck with the same kind of anchor points as the castle tower, i.e- metal loops to tie them down to, usually in such a way you can still turn to aim easily (i.e- a single loop of rope through two hoops so lengthening one side shortens the other).

I'd think the same would be true of a War Carriage on a large creature; the platform would need to be sturdily built, and well secured to the creature, and should have the necessary mounting for securing any siege weapon you want to put on there. The creature itself could also be a factor; this is why I mentioned maybe having the creature go stationary or glide when the siege weapon is being fired, as this can represent a dragon levelling out to give a better shot with a ballista, or a gargantuan beast with a trebuchet hunkering down to brace against the force of the shot.

I think it makes reasonable enough sense to work both thematically and realistically; we don't have many real comparisons we can make, but elephants have been used in the past to carry ballistas that could be fired from their backs, so it's not without precedent. Of course you'll need to decide for yourself in your games whether a tebuchet makes sense on a flying creature for example (probably not), but a Dragon Turtle used as a naval vessel could justify it, as the shell could maybe take the stress of firing without any extra reinforcement.

Quote from CarcosanHerald >>

Imagine if someone used these templates for an Urban Arcana-style campaign. Look me in the eyes and try to tell me, with a straight face, that a red dragon with rocket pods and heavy machine guns strapped to it wouldn't be the most metal creature ever.

Fox One!

I have a few I'm proud of:

A CR 6 mage slayer (based on the monster slayer ranger)

An undead troll that releases explosions of necrotic energy

A Stalker of The Night, a Gloomstalker/assassin mix that is super deadly

And a few others. Check them out by filtering by user and selecting "Thunder5077"

Quote from SjtSquid >>

Honestly, I probably homebrew way more than is necessary, but occasionally I end up with something that works way better than expected. My best homebrew monsters include:

 

A modified water/ice elemental pair that had attacks that were only usable if the target was standing on water/ice, some terrain changing abilities.

 

A group of wind elementals that you could take a 5ft knockback instead of taking the damage from their attacks. (The floor of the room was illusiory in places, making this a risky proposition.)

 

A magic-consuming ooze for a Ravnica one-shot that got faster when it was hit with magic, and had Absorb elements at will.

 

Anyone else got any homebrew creations they are particularly proud of?

I have a few I'm proud of:

A CR 6 mage slayer (based on the monster slayer ranger)

An undead troll that releases explosions of necrotic energy

A Stalker of The Night, a Gloomstalker/assassin mix that is super deadly

And a few others. Check them out by filtering by user and selecting "Thunder5077"

If there was a merchant who sold these, how much gold would you say these would cost?

I generally do not have an issue with smaller siege engines and after I read the trebuchet I had realized that the info I had seen was for larger sized units, but even then their is a lot more involved then attachment to the ground (preping the ground for repeated fire of the weapon). 

Also in general just making the whole thing from metal and or magical material may not solve the issues. But if an author provides a idea then explaining how that idea can be made to work in a game is generally better. Why? You are trying to provide guidance to GM's and players on how to run a game and be an example of how to introduce ideas into a game. If you simply say "Magic Baby" is the answer the question from the players quickly becomes why cannot we use "Magic Baby" to solve our problems and only the GM can?

Note: I am no expert on D&D 5th spells but to me it looks as if I would use 2 wishes to make a trebuchet work as a weapon on a platform. One to nullify the forces and one to secure it to the platform. When explained that way IMHO it provides context to both GM's and players who want to use such devices in their games. 

Have I seen this type of thing in real life? Yes about 4 years ago a group of people were talking about using lava (because lava did 20d6 damage a round) to build structures and how to make it happen. It was a spell to put the material in stasis then transport the blocks, then strengthen the blocks, then be able to renew the spells without them failing and all of the other stuff that went a long with the project. after talking about it I think the posters had a better idea as to what had to happen instead of just take the highest damage environment and place it in stasis for a trap and not plan for it lasting longer than a week (ie the players are only going to only be at the location for a week so that is how long it has to last).

Have I done the things above, yes I started gaming in 78 and have done lots of things (both positive and negative) while a GM and player and I look for was to make my gaming better (that can be dependent of the type of game and setting, ie a 1-3 week battle royal where all players are against each other and anything goes is a different set up vs a game to last a year or just create PC's for a module)

MDC 

Me: *Sees this article* "cool"

3 seconds later:

"I know what I must do..."

What I do:

- Purple worm with guns

nice

yes