Can a Battle Smith artificer's Steel Defender be used to hurl Magic Stones?

Question

When designing a Battle Smith artificer's Steel Defender (E:RftLW, p. 61), the feature description states:

You determine the creature's appearance and whether it has two legs or four; your choice has no effect on its game statistics.

If I were to create it to resemble a Medium-sized Ape, could it throw the pebbles imbued with magic that I create using the magic stone spell?

I can imbue 3 stones as a bonus action, and then drop them beside the Ape before attacking. The next turn, the Steel Defender could pick them up and throw.

Obviously, this is a level 3 mid-game question. 1d6+5 just seeing do much at higher levels.

Answer 1

Yes, it can take any action (as the feature description now clearly states)

E:RftLW received an errata in 2020 that updated the description of the Steel Defender feature, which now reads (emphasis mine):

[...] but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take another action. That action can be one in its stat block or some other action.

The new wording is intended to be generic and flexible, the errata was precisely to fix the old restrictions. Rules designer Jeremy Crawford states in an unofficial tweet that this even can allow the defender to use magic items:

A D&D creature can use magic items, unless its anatomy or a rule precludes such use. For example, the steel defender is a creature that can reasonably use many different magic items.

As well as using more permanent magic items, per this unofficial tweet:

The magic item attunement of your companions has no effect on the number of items you can attune to.

Answer 2

No, it can only use the actions in its statblock

The text for the Steel Defender feature reads:

It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take one of the actions in its stat block or the Dash, Disengage, or Help action.

The feature specifies that the action must be from its statblock.

The description of the Magic Stone spell reads:

You or someone else can make a ranged spell attack with one of the pebbles [...]

It allows someone other than the caster to use the stone, but it still requires you to take the Attack action to do so. The rule that allows someone else to use the stone is general because it refers to everyone who is not the caster. The rule regarding the Steel Defender is specific because it only applies to the Artificer's use of a feature as a bonus action. A general rule allowing other creatures to use the stone cannot overrule the specific rule defining the Artificer's use of a feature.