Just how creative should the DM let the Artificer be? One of my players is a guy who thinks way too hard on how to solve problems he's not meant to 'Solve' as a player.
For example, I have a little set-piece in place for my campaign setting where there are roaming clouds of illusion magic that will appear at random times around the region. These clouds effectively have the magical power of 9th-level illusion magic violently swirling within them, causing all kinds of chaos when they appear.
They are meant to be a hazard that the players are meant to avoid, but my Artificer player thinks differently. He surmises that with all his tool proficiencies like Smith's tools, Tinker's tools, Alchemy supplies, etc., that he should be able to build any kind of contraption he wants given time. I tried to explain that doing so would grind the game to a halt, as he would need to study for years in game time to come close to building the 'giant magical vacuum' that can suck up the illusion storms, and he wouldn't even be able to determine whether it would work or not.
This is only one of many hypothetical arguements we've had in the past, and I would just like a reference to point to in the future if he ever picks to play Artificer again:
Exactly how much of the hypothetical creativity should be allowed to actually happen when a player uses meta knowledge to build machines in a D&D setting? What power do artisan's tools actually have in the hands of an Artificer?
Best Answer
Artisan Tools function more-or-less the same for Artificers as they do for other classes; with a few perks
Any character with proficiency in Artisan's Tools is able to use those tools to craft items, magical or non-magical.
The non-magical rules are introduced in the Players's Handbook, expanded upon to include magical items in the Dungeon Master's Guide, and then revised/rebalanced in Xanathar's Guide to Everything.
Emphasis mine, the relevancy of which should become quite apparent.
Artificers have two particular perks as they relate to these rules: the first is that they have a special feature, the details of which are decided upon by their subclass, that enables more efficient crafting than other characters:
The other major perk is their ability to at sunrise "infuse" items so that they behave as though they were magic items, but for our purposes we don't need to think about that perk.
The important part is, while their ability to do so is greatly improved over that of other classes, Artificers aren't strictly capable of making better or more powerful magic items than anyone else: they just have an inherent affinity for doing so.
So about their plans to subjugate 9th level Spell Effects...
As DM, there's good reasons to at least encourage the Artificer in question to try to tackle this. It might lead the campaign in an interesting direction, or create new ways for you, the DM, to interact with the narrative of your story.
But, naturally, there needs to be limitations. And there are some very good hints to help us work out how stringent those limitations might have to be.
If the clouds are "Level Nine Spells", an object capable of subjugating them probably also needs to produce a "Ninth Level Effect"
This seems perfectly reasonable, yes? I'd like to think the player trying to do this will respect this as well.
There's also precedent for this: the spell Imprisonment specifically says "A dispel magic spell can end the spell only if it is cast as a 9th-level spell, targeting either the prison or the special component used to create it." (PHB, pg. 252), so it's not unreasonable to rule that other ongoing effects of "Ninth Level Power" might have similar restrictions.
So what is required for a player to create an item that can produce a "Ninth Level Effect"? Well, there's two rules we'll want to look at: the restrictions on crafting magic items of various rarities, and the rules for creating whole new magic items to place in a campaign.
So these two tables in conjunction with each other tell us some very important information:
So in total, this Artificer (or any character for that matter) is probably going to be required to be at least level 17 before they can successfully create the kind of "Magic Cloud Vacuum" they intend to create. You might tweak these rules for your own purposes (maybe Artificers get access to higher level item recipes at a lower level? Maybe the clouds are more like sixth or seventh level instead of ninth?) but at least by the standards set by the game itself, it's certainly outside the capabilities of a low level character.
Sidebar: per the way the rules are written, if such a character wanted to produce an item that actually produced a Ninth Level spell, not just a "Ninth Level Effect", they'd need to be able to both cast the spell and consume a Ninth Level Spell Slot—which Artificers never get. Personally, I would handwave that for Artificers, since it feels thematically inappropriate for a Wizard to be more capable at producing Magical Items than an Artificer, but in general it is a good rule to follow.
Conclusion
Personally speaking, as DM, I prefer to be as permissive as possible when it comes to player decisions, unless it's obvious that they're abusing the rules and in doing so making the game unfun for everyone else. It's not obvious that that's what your player is doing—from your description it just sounds like they're really enthusiastic about the possibilities of a character that can create magic items—so I think it's okay to help them reach a point where they might be able to do something like this. But you need to make it clear that that's not going to happen for a new character.
Like illustrated above, there's a set of relatively reliable rules that tell us that what they're trying to do is theoretically plausible, but they should be required to at least fulfill the minimum requirements. And if you use these rules as-is, that means they need to reach level 17.
So if your campaign runs for long enough that they get to or near level 17, you should go ahead and set them up for their quest to build the magical Cloud Vacuum that will let them do exactly that. Just make sure it's clear to them that that's a long-term goal, not something they should expect to be able to do as a new or even moderately veteran character.