Crebain and shadow effects
In describing the various parts of encounter cards, the rules say (on page 6):


  
  Shadow Effect Icon: If a card has a shadow  effect, that effect is denoted by this icon, which also serves to separate the shadow effect from the card’s in play effect.
  


This suggests that encounter deck cards have both "in play effects" and "shadow effects".  Since Crebain does not differentiate between the two classes of effects, it follows that with Crebain in the staging area, shadow effects cannot be cancelled.