I am trying to figure out if the Executioner assassin (Heroes of Shadow) applies its dexterity to its melee basic attacks. The Attack Finesse Class feature says: You can use Dexterity instead of Strength for your melee basic attacks. Does this mean substitute dex only for the attack roll and use strength for the damage roll as normal, or use dexterity for both attack and damage?
Both attack and damage
Where it says "use X" for your attacks, replace all instances of the original stat with X. In the cases where it is specifically for attack bonus (like melee training) it'll explicitly call out the difference.