Now this is just a question that I thought of randomly and I couldn't find an answer with a preliminary Google search.

With most artifacts, you can roll on random beneficial and detrimental tables, and in the Minor Beneficial Properties Table, it has some abilities where you can cast a spell of the DM's choice using the artifact. My question is, in a spell like Heroism it states that you give someone temporary HP based on your spellcasting modifier, and if a character without a spellcasting class (or spellcasting ability for that matter) uses that ability, is there like a base spellcasting ability that is used?

I would honestly just assume that it would be DM's choice but I felt like asking the question since, in a certain way, it is entirely possible that it could happen in the game normally.

I've always been a proponent of making basic magical abilities not granted by any particular class key off of Constitution. It's a fairly class-neutral attribute, nobody is going to be jacking it up to 20 in Tier 1 or 2, but nobody is going to be dismayed (cough cough Dragonborn) that their special ability requires a stat that their class tells them to dump.

Otherwise, it's inconsistent enough which attributes racials key off of, that I think a kind DM would be justified saying "whatever your class uses to set the DCs of its abilities, use that." There are very few classes that truly have no DC abilities in their kit (maybe a couple of Fighters, Barbarians, and Rogues?) and for those I would again recommend Constitution, rather than Strength or Dexterity. 

The Book of Vile Darkness uses a fixed DC of 18 for the Dominate Monster spell.

This is the same DC given to the Hand and Eye of Vecna as well as the Orb of Dragonkind.

So you can probably just skip the ability score and just put in a fixed modifier.

I'm not a big fan of fixed DCs on items either. I've been catching up on Critical Role recently, and was just watching an episode where Laura was all geared up to use a Wand of Smiles but felt pressured not to waste her turn because its only a DC 10 (note, not because making the enemy smile would be a waste of a turn). It came off like it definitely wasn't an in-character decision but rather a mechanically imposed one that limited her role playing. It doesn't seem like items having set DCs accomplishes much in terms of streamlining play (you end up having to sift through your character sheet every time you use an item ability because the DCs are all different), doesn't seem necessary for balance (5E doesn't have expected magic items that track level progression like prior editions did, so there's really no telling what Tier you'll be receiving any given item in), and just sort of frustrates and sabotages players. 

Quote from Chicken_Champ >>

I'm not a big fan of fixed DCs on items either. I've been catching up on Critical Role recently, and was just watching an episode where Laura was all geared up to use a Wand of Smiles but felt pressured not to waste her turn because its only a DC 10 (note, not because making the enemy smile would be a waste of a turn). It came off like it definitely wasn't an in-character decision but rather a mechanically imposed one that limited her role playing. It doesn't seem like items having set DCs accomplishes much in terms of streamlining play (you end up having to sift through your character sheet every time you use an item ability because the DCs are all different), doesn't seem necessary for balance (5E doesn't have expected magic items that track level progression like prior editions did, so there's really no telling what Tier you'll be receiving any given item in), and just sort of frustrates and sabotages players. 

 I disagree for a number of reasons that I don’t have the energy to get into at the moment. I’ll get back to you about it though.

For Artifacts, the DC is always going to be very good, and conceptually, it represents the influence of a very powerful entity. In many cases, the Fixed DC of an Artifact will meet or exceed the highest modifier of the player who received it, so you would actually be penalizing the player by basing it off of their own Spellcasting Attribute, whatever that would be.

In the case of regular Magic Items, a Fixed DC can be extremely important. A common magical item could have a very potent effect that is balanced for a low DC, but as soon as it is allowed to scale, causes the item to outshine actual class abilities and spells.

A Wand of Smiles has no mechanical benefit according to RAW, so it's not as much of a risk. I'd be perfectly fine Homebrewing a solution for a character like Jester, especially if it required expending a spellslot to empower the Wand. The actual impact it has on the game is entirely DM discretion, so it being a wasted action to use in combat really has nothing to do with the Save DC.

While you are attuned to the book and holding it, you can use an action to cast the dominate monster spell on an evil target (save DC 18 your Spell DC, with an additional +2 bonus). You can’t use this property again until the next dawn.

There, how hard was that? Now if for plot reasons you have the Book in a low Tier it doesn't break the curve of realistic saves for opponents, while still standing out as unusually powerful regardless of what level you are using it at. For a crappy common item, just do the same in reverse ("your Spell DC, with an additional -2 penalty"). 

Common and Uncommon magic items can and do get handed out in all tiers of play. Some of these items (e.g. Doss Lute) anticipate that, and reference the character's Spell DC so that they'll remain relevant regardless of tier. Others (e.g. Circlet of Blasting) hamper themselves by setting a DC or attack bonus that is only going to be relevant at a certain level, and transform into vendor trash once you're past that or break balance if handed out prior to that. That's poor design. 

That just reintroduces the issues of how non-casting classes should determine their Spellcasting Attribute.

For a Barbarian who has dumped both Charisma and Intelligence, you've now got a Magic Item that probably grants a whopping Save DC 5, which makes wielding even artifacts (DC 9) pointless.

If you let players use their highest stat as their "Spellcasting" stat, then you've got a whole 'nother bundle of issues to sort out. If you fix it to one particular non-mental stat, then you've just created a massive bias in character creation.

I never said they should just use their highest stat, I specifically proposed that the default be Constitution, or whatever stat their class provides that they use to set their DCs. And that is an almost entirely separate issue (though admittedly one more germane to the original post) than whether magic items with static DCs are poorly designed for remaining relevant through all tiers of play (which we're only talking about because you introduced it into this thread). 

Magic Items aren't supposed to remain relevant to all tiers of play. "It's not a bug, it's a feature".

Some do, but a lot of low level items are designed to be made obsolete as characters grow into their higher level abilities, so that players can show off their strengths.

If items like the [Tooltip Not Found] and Eyes of Charming were allowed to scale, then you would have weak wizards with the ability to grapple as well as the Barbarian, every round, or Barbarians who can Charm dragons. (Keep in mind that if the Barbarian's DC is based off strength, an item like the Belt of Storm Giant Strength would give him a +9 modifier)

Taking Spellcasting out of mental stats compromises a LOT of important balancing mechanics.

There is a lot of potential for giving special dispensation to players for a Favored Item on a case by case basis, but as a blanket rule, it's dangerous.

There is literally no such thing as a low level magic item. I am on my phone and can’t look up quotes very easily right now but see the starting play at higher level section as well as the DMG chapter on magic items and you will find nothing that suggests an  uncommon item is not appropriate for a 17th level character.

"Low Level" means "items predominantly available at low levels" typically due to limited funds.

You're absolutely right. There is nothing wrong with a 17th level player having an uncommon item, but there is also nothing saying that an uncommon item is "supposed" to remain relevant. Some will, some won't.

If you’ve ever played Destiny 2 the whole point it you start out collecting green items and then move through blue items until eventually you have all purple items and a gold one. 5e is basically the same.

I wouldn't take it that far. Weapons in Loot collecting games are usually just straight upgrades with a variety of properties peppered in.

5e has plenty of items that remain relevant for high level play, like Cloak of the Mantaray to gain a swim speed, and elemental weapons to swap out based on the adventure.

The only real issue tends to be with items that directly impact combat, like inflicting a Condition, or dealing damage. At low levels, the players haven't grown into their unique roles, so it helps to have some back-up options. At higher levels, class features usually begin to fill in the gaps.

https://www.dndbeyond.com/sources/dmg/a-world-of-your-own#StartingatHigherLevel 

In a "standard" campaign, a 17th level character should have roughly two Uncommon items and one Rare to be on-curve. So, no, you should not have nothing but purples and golds. If Uncommons don't have a way of remaining relevant at 17th level, then the right hand of design doesn't know what the left is doing. 

Quote from Chicken_Champ >>

https://www.dndbeyond.com/sources/dmg/a-world-of-your-own#StartingatHigherLevel 

In a "standard" campaign, a 17th level character should have roughly two Uncommon items and one Rare to be on-curve. So, no, you should not have nothing but purples and golds. If Uncommons don't have a way of remaining relevant at 17th level, then the right hand of design doesn't know what the left is doing. 

 Ding ding ding!!! You just won the cupie doll!

Heeeeeeeeere’s WotC!!! 

Quote from Minat0thelim3t >>

Now this is just a question that I thought of randomly and I couldn't find an answer with a preliminary Google search.

With most artifacts, you can roll on random beneficial and detrimental tables, and in the Minor Beneficial Properties Table, it has some abilities where you can cast a spell of the DM's choice using the artifact. My question is, in a spell like Heroism it states that you give someone temporary HP based on your spellcasting modifier, and if a character without a spellcasting class (or spellcasting ability for that matter) uses that ability, is there like a base spellcasting ability that is used?

I would honestly just assume that it would be DM's choice but I felt like asking the question since, in a certain way, it is entirely possible that it could happen in the game normally.

 
This is covered in Chapter 7 of the DMG under Activating an Item. (emphasis mine)

A magic item, such as certain staffs, may require you to use your own spellcasting ability when you cast a spell from the item. If you have more than one spellcasting ability, you choose which one to use with the item. If you don't have a spellcasting ability - perhaps you're a rogue with the Use Magic Device feature - your spellcasting ability modifier is +0 for the item, and your proficiency bonus does apply.

So if you don't have spellcasting ability then:

Spell Attack: 1d20 + your prof bonus

Spell Save DC: 8 + your prof bonus

For Heroism, you'd not grant any temp HP, you'd just make them immune to being frightened.

Quote from Chicken_Champ >>

https://www.dndbeyond.com/sources/dmg/a-world-of-your-own#StartingatHigherLevel 

In a "standard" campaign, a 17th level character should have roughly two Uncommon items and one Rare to be on-curve. So, no, you should not have nothing but purples and golds. If Uncommons don't have a way of remaining relevant at 17th level, then the right hand of design doesn't know what the left is doing. 

That "curve" also includes ~22,000 gold, which can be used to buy approximately 100 Uncommon items (or ~10 Rare items) on top of those already included. If all of those uncommon items scaled, that character is not just powerful, but a walking armada. 

 Some of those Uncommon items (I'm looking at you Javelin of Lightning) are already terrifying just due to being spammable in large numbers.

Nah. “Unless you decide your campaign works otherwise, most magic items are so rare that they aren’t available for purchase.”