Forum:Valhalla vs Oppression..confusing..

Ok...where to begin. I heard that when activating Valhalla, Hall of the fallen from the hand without activating it's effect immediately, oppression cannot be activated(of course i know about that), but if you use the effect after valhalla is already face-up on the field, oppression still cannot be activated. I got this tip from a guy on youtube http://www.youtube.com/watch?v=la-AVKLJN_g  He explains in the video in 2:15. Suppose its a loophole. I don't know.