The imp unlocks a hatch when the quest is complete, allowing you to get the summoning doll. A doll's stats are determined by the difficulty level of the game the first time they are summoned (by clicking on the doll in your inventory). If you are playing on easy or action, you can get a slightly stronger doll by switching to tactical before summoning each one (if you switch to hardcore you can not lower the difficulty level again... at least not through the game options).
