Laboratory: 2 draws, 1 action is just too easy to stack with itself. Not necessarily banned, but certainly never play on the same table as Festival.
Possession: Aside from lengthening the user's turn and preventing the victim from planning ahead, it punishes owning a deck with strategy, as someone may use your well-thought-out hand (multiple times, if they are able to play more than one Possession) to buy Provinces. Meanwhile, you are unable to use this card to any real end yourself if the person to your left does not have a solid deck.
Scrying Pool: Sheesh. Might as well say "Cycle through your entire deck." Fucking with your opponent's deck is just gravy. The time you waste will annoy them more than anything.