The Mechanist

Character Concept

Planning

There are two ways we could get the most out of this spell (without asking one of our party members to use their action every round). First, we could cast the spell on a familiar. This is amazing if you can pull it off. Familiars cannot take the Attack action, but Dragon's Breath is explicitly not that. Jeremy Crawford has confirmed that familiars can activate Dragon's Breath, as well. Familiars take their own turn in combat, can fly if you want them to (pick the Owl), and commanding them is a free action! Keeping them alive can be tricky against most enemies, though, and if they die, there goes your action economy. I would only use Dragon's Breath on your familiar if you are confident they will not be attacked like if the enemies only have melee attacks and can't fly.

The second and likely more reasonable option, is to cast Dragon's Breath on a pet of some kind and command it with a bonus action. This limits our class options significantly unless we want to delve into MAD (Multiple Ability Dependence) territory. There are no Charisma-based classes that have constant pet companions aside from a Pact of the Chain Warlock and they just get a fancy version of a familiar which is about as easy to kill. I've heard some suggestions that an Imp's invisibility does not break from activating Dragon's Breath. That seems like a generous interpretation of the rules and even if it is true, technically just means your Imp gets attacked with disadvantage and can still only probably take one hit before dying. Technically, the College of Creation Bard does sort of get a pet with their Dancing Item but the Dragon's Breath spell specifies the target must have a mouth so that's probably a no-go unless your DM allows a statue or something to be a valid target. Seems unlikely.

This leaves us with the Intelligence-based classes. Unless your DM is willing to let your Order of Scribes Wizard's Manifest Mind ability to count (I wouldn't), then your only remaining option is the Battle Smith Artificer. There's a few reasons why this causes some issues, but it also opens up some nice opportunities for this build that we wouldn't have with most of the other options. CON save proficiency is going to be huge for keeping Dragon's Breath active and the basic infusions give some nice boosts to AC and attacks. Unfortunately, unless we are planning on taking a lot of Artificer levels, we are going to have a pretty weak companion that may not be much better than a familiar in terms of survivability. It's going to be a problem, but I have a solution, just wait.

Level 1

OK, so if you're still with me, we are going to start as an Artificer and switch to Wizard once we get our pet. Then we will focus on Wizard to maximize our spell levels for maximum upcasting!

For race, I suggest Custom Lineage. This works really well for us for a few reasons. First, we can boost our Intelligence by 2. We only really care about INT and CON. And our CON doesn't need to be too high for us to maintain concentration for reasons that will become clear. Using point-buy stats, I suggest:

• STR: 8
• DEX: 8
• CON: 14
• INT: 15 (+2)
• WIS: 12
• CHA: 8

Our Custom Lineage feat will be Fey Touched (INT). This will put our INT at an 18 to start and give us access to Misty Step. More importantly, we can take Dissonant Whispers as a free once per day spell which we can then cast using spell slots. This will be important later. Also, we want to choose to be Small size.

For spells, pick whatever you prefer. Fire Bolt or Shocking Grasp will be our go-to spell in combat for a few levels, depending on where you want to stand. Guidance is great if no one else has it but otherwise take Mending.

Levels 2-3

At level 2, things start to kick off. Infusions are going to be a big deal for us but since we're only taking a few levels of Artificer, we won't get very many. Enhanced Weapon, Enhanced Defense, Enhanced Arcane Focus, and Mind Sharpener are my choices. You could probably swap out Enhanced Arcane Focus for something else if you need to but it might come in handy at low and high levels. Put Enhanced Arcane Focus on a wand and Enhanced Defense on your shield.

At level 3, we choose our Artificer subclass. We are taking Battle Smith as I've already explained. Just about everything here is perfect for us. Battle Ready allows us to use INT to attack with magic weapons (infused weapons count). Shield is a fantastic survivability spell that will keep us from having to make concentration checks. And we get the Steel Defender that this whole build revolves around. We are small size so we can ride our medium size Steel Defender.

We probably also want to take this opportunity to swap out our attack cantrip for Booming Blade. Swap out Enhanced Arcane Focus for Enhanced Weapon on a longsword or morning star. From now on, we're going to be a front-line fighter. If at some point in the future, you get a magic weapon, drop Mind Sharpener on your armor for free concentration checks.

Levels 4-7

Now we start taking Wizard levels. At level 4, we want Find Familiar. It's great for its versatility but also in some situations it will be even better than our Defender for Dragon's Breath. Also pick up the Mending cantrip if you don't have it because keeping our Defender healed may already be a problem.

At level 5, our survivability is going to get a boost because we are going to take the School of Abjuration tradition. Shield will activate our Arcane Ward and we'll get a decent pool of HP on top of our own. Oh, and if the damage doesn't break our Ward, we don't have to make a concentration check. Nice!

Level 6 will mark the point where we FINALLY get access to the Dragon's Breath spell. This is a game-changer for a few reasons. At the beginning of combat we can cast this on our Defender (or familiar) and ride them into combat. They can breathe whatever element we want on our enemies and as long as this hits at least 2 targets, the damage is quite nice. And that's only our bonus action. Then we can use whatever spell we want but my favorites are Booming Blade and Dissonant Whispers. It's important to remember that forced movement from Dissonant Whispers DOES cause opportunity attacks. Moving your Defender near an enemy that your ally is fighting and casting Dissonant Whispers on the enemy will trigger opportunity attacks from your Defender and your ally. It's a great way to boost your party's damage and they'll love you for it. You can also use it to try to group up enemies for your Dragon's Breath.

Level 7 is almost as big of a level as 6. You get an ASI/feat here and I can't take War Caster hard enough. This is action economy at its finest. Now when your melee opponent fails to save against Dissonant Whispers, you can attack them with Booming Blade, your Defender (and possibly ally) gets an attack, they have to move away, your Defender can move into range for Dragon's Breath, and they have to decide whether to sit there and take it or move to attack and take damage. This is huge. Really solid damage and control. Alternatively, drop Hold Person on them and stop them in their tracks for some guaranteed critical hits. It's like getting 3 actions on your turn.

Levels 8+

At this point, the build is basically finished. There's only one other choice to make: How do you want to keep your Defender alive? At this level, their 21 HP is probably becoming a big problem. This is the biggest weakness of the build. Defenders are not very survivable even if you only take Artificer levels. Thy have a built-in heal and can be healed with the Mending spell between fights, but eventually you hit a wall where they're just getting annihilated in one hit. There's only so much that you can do to keep them out of harm's way.

The big question is: When is this adventure going to end? If you're not going to get to level 20 (of course you aren't), then I suggest picking up one last level of Artificer at level 8. This will give the Defender more HP, but more importantly you'll get another ASI/feat and you can take Mounted Combatant. This is why we chose to be small at level 1. This feat allows us to take attacks for the Defender and gives the Defender a chance to take no damage against a lot of spell effects and traps. In rare circumstances we also might get advantage on attacks but that's not going to happen very often with a medium size mount.

If you are certain that eventually this character will be level 20, then it's really difficult to justify missing out on 9th level spells for this. At 6th level Wizard, you can use your Ward to protect your Defender if you have to, but it takes your reaction. This will help, but expect your Defender to die a lot. It just takes a 1st level spell slot to bring them back, but you'll save that casting of Dragon's Breath.

Analysis

There's some minor considerations here regarding the rules for mounted combat, but I suspect that most DMs will allow you to ride the mount, moving on your turn, and let it take its action right after your turn. I think this is the correct interpretation of how these rules interact. It's how I would rule it and it is how other DMs I've talked to would rule it. So that's how I'm counting it here.