Target: one creature
Attack: Intelligence vs. Fortitude
Hit: "1d10 + Intelligence modifier necrotic damage, and the target is weakened until the end of your next turn."[PH:160]
The "Class Compendium: The Arcanist" article in Dragon 401 added the necromancy keyword and half damage on a miss to ray of enfeeblement. Previously, ray of enfeeblement had no effect on a miss. The December 2011 update finalized these changes.