After killing Isobel in act 2 and resting you receive your slayer form and with it the achievement "Embrace Your Urge". The achievement's description reads: "Become Bhaal's ultimate weapon - become his Slayer." Steam users may stumble upon this description in the post game summary after unlocking the achievement. The connection between the Dark Urge and Bhaal is a story revelation that takes place during act 3, when the Dark Urge's memories start to return. The player may figure that a murderous inclination might be connected to the god of murder and there may be other hints as well, however the connection to Bhaal is not definitively revealed during act 2 as far as I can tell. The Butler is very vague as to the source of the slayer form.
It seems that this act 2 achievement contains a spoiler for act 3 and the reference to Bhaal should be removed.
