I'm playing a dwarf deck. Let's say I have 5 units in my discard pile. If I play the Slayer Oath (Target unit gains 1 P for every unit in your discard pile) then play Reclaiming the Fallen (put all units in your discard pile into one of your zones) does the unit I targeted with Slaer Oath still gain the additional 5 P or is this a constant effect thing were he gains 0?

This is one of those things that goes all the way back to "How does Toxic Hydra work?" Cool people like me think that Toxic Hydra does not create a constant effect but is a one shot thing, but that was never clarified in writing. So the analogue here is "Does Slayer Oath create a constant that the unit gains P = # units in discard pile that is on until the end of the turn? Or does it simply check # when you play it?" I would play it's a one time thing, again because I am cool, but coolness has no weight in rule interpretations and I have been wrong in the past. Many, many times.

For what it is worth: I was playing a game with Brad Andres present and he ruled that Toxic Hydra created a constant effect. That means that using the same logic he employed in a most uncool fashion, the Slayer Oath would result in the unit gaining 0 P after you play Reclaiming the Fallen.

I fully agree with you HappyDD, as does our small group of players. (total of 6)

Wait, you agree with the cool interpretation or the uncool one? Be cool.