A Transmutation Wizard has decided to make a Transmuter's Stone and has chosen the property of granting Darkvision. What happens when a blind character has this stone in their possession?
Darkvision is unfortunately useless to a blind person. Weirdly, when a race gets Darkvision, it's described in that race's entry. But the Transmuter's Stone says this:
Darkvision out to a range of 60 feet, as described in chapter 8
So if we find the entry on Darkvision in chapter 8 (PHB, page 183):
Within a specified range, a creature with darkvision can see in darkness as if the darkness were dim light, so areas of darkness are only lightly obscured as far as that creature is concerned.
Blind people can't see in dim light, so seeing in darkness as if it was dim light doesn't actually help them at all.
In the rules, being blinded results in the following:
A blinded creature can’t see and automatically fails any ability check that requires sight.
Therefore, it does not matter if the creature gains Darkvision, because they still can't see, and automatically fail any task involving sight.