I'm curious if a sentient magic item can be counted as a creature for spells such as Scrying.
No, it can not be by RAW
The Scrying spell states (emphasis mine)
You can see and hear a particular creature you choose that is on the same plane of existence as you. The target must make a Wisdom saving throw, which is modified by how well you know the target and the sort of physical connection you have to it. If a target knows you're casting this spell, it can fail the saving throw voluntarily if it wants to be observed.
Instead of targeting a creature, you can choose a location you have seen before as the target of this spell. When you do, the sensor appears at that location and doesn't move.
By RAW, the target should be either a creature or a location, not an item, even if it is a sentient magic one.
Moreover, the section of sentient magic items in DMG does not mention this possibility. In the 3rd paragraph (pag 214) you can find nonetheless
Sentient magic items function as NPCs under the DM's control.
It seems that this may allow one to consider a sentient item as a creature, since it is written that it functions as an NPC, but actually this sentence is just for the DM, in order to give directions on how to rule these items in game.
Indeed, there are other spells that support the above reading of the rules:
- Locate Object and Locate Creature, for example, that are specifically designed for items and creature, respectively. Moreover, Locate Creature says (emphasis mine):
If the creature you described or named is in a different form, such as being under the effects of a polymorph spell, this spell doesn't locate the creature.
Hence, if a creature is transformed into an object via True Polymorph, the spell fails because the target is in a different form.
A monster with truesight can, out to a specific range, see in normal and magical darkness, see invisible creatures and objects, automatically detect visual illusions and succeed on saving throws against them, and perceive the original form of a shapechanger or a creature that is transformed by magic. Furthermore, the monster can see into the Ethereal Plane within the same range.
- See Invisibility explicit mentions creatures and object:
For the duration, you see invisible creatures and objects as if they were visible, and you can see into the Ethereal Plane. Ethereal creatures and objects appear ghostly and translucent.
These spells make explicit their targets: creatures, items or both.
As Written: No.
An object may have certain qualities which make it seem like a creature, however, it is still an object. In the magical world of DnD some objects can speak, move around, and every have an embedded consciousness. But until they are given a full stat block identifying them as a creature, they are still an object.
For example, in the DMG creation rules states:
If you determine these characteristics randomly, ignore or adapt any result that doesn’t make sense for an inanimate object.
Indicating it is still, an inanimate object, despite its unique qualities.
That said, there is at least 1 sentient item in which the consciousness can be released into a full creature.
The Shield of the Hidden Lord in Baldur's Gate: Descent into Avernus.
Finally as a DM you always have the option to allow spells to work even if they do not mechanically work as written. For example, many cantrips only target creatures, however it is not uncommon for DMs to allow you to say "Eldritch Blast" a door or window.