You can only get 1 copy of "Polymerization" when you discard "King of the Swamp" from your hand.
You can activate the effect of "King of the Swamp" even if all 3 of your "Polymerization" cards are in your Graveyard.
If "King of the Swamp" is selected for the effect of "Prohibition", you cannot use either of its effects.
Discarding this card is a cost.
If you use "King of the Swamp" as Fusion Material from your hand, you do not get to activate its effect to search your Deck for "Polymerization".