If "Thunder King Rai-Oh" is face-up on the field, then you cannot activate "Pot of Duality". Also, if an effect is Chained to "Pot of Duality" and Special Summons "Thunder King Rai-Oh", then when resolving "Pot of Duality" you still reveal the top three cards of your Deck. You select one card to be added to your hand and send it to the Graveyard instead, and shuffle the remaining two cards into your Deck.