This was inspired by Can Bigby's Hand attempt Strength and Dexterity saving throws? (and in fact this first bit was copy-pasted from it, but with different bold emphasis):
The spell description for Bigby's hand on PHB p. 218 (listed as arcane hand in the SRD) states:
The hand is an object that has AC 20 and hit points equal to your hit point maximum. If it drops to 0 hit points, the spell ends. It has a Strength of 26 (+8) and a Dexterity of 10 (+0).
The Strength score is used for a few of the hand's specified uses (bold emphasis mine):
Forceful Hand. The hand attempts to push a creature within 5 feet of it in a direction you choose. Make a check with the hand's Strength contested by the Strength (Athletics) check of the target. […]
Grasping Hand. The hand attempts to grapple a Huge or smaller creature within 5 feet of it. You use the hand's Strength score to resolve the grapple. […]
Interposing Hand. The hand interposes itself between you and a creature you choose until you give the hand a different command. The hand moves to stay between you and the target, providing you with half cover against the target. The target can't move through the hand's space if its Strength score is less than or equal to the hand's Strength score. If its Strength score is higher than the hand's Strength score, the target can move toward you through the hand's space, but that space is difficult terrain for the target.
But what is the Dexterity score for? It's not mentioned anywhere besides stating that it's 10 (+0). It seems strange that they'd include it (and not CON, INT, WIS or CHA) if it isn't actually relevant, so that it is included implies is has a use. If that use isn't for making saving throws, then what is it for?
Note: This is not a "designer reasons" question; I accept that it is included in the spell's description, whatever their reasons. I am not looking for designer quotes or speculation on why they included it. My question is, given that it is included, what is its purpose? What are ways, within the rules that we have, that this ability score would come into play for Bigby's Hand?
Best Answer
The Dexterity score could be used to make Dexterity checks.
The description of Bigby's Hand includes this sentence in the first paragraph:
Everything that follows in the spell description can be read as exceptions to this. That is, in addition to being able to mimic the movements of your hand, Bigby's Hand can punch, grasp, and interpose according to the spell description. You can also do ordinary hand-things with it, like opening a closed portcullis, or unfurling the sails on a ship. If you attempt a task in this way that requires a Strength check, you use the hand's Strength of 26. And if you attempt a task that requires finesse, you would use the hand's Dexterity of 10.
For example, if someone nearby a Bigby's Hand drops a valuable potion, you might use your reaction to catch it with the Hand. The DM would almost certainly ask for a Dexterity check, and you would make it using the Hand's Dexterity bonus of +0.