Use King of the Swamp depending on what you need. You can send it to the Graveyard to get Polymerization or use it as a Fusion Substitue. It's recommended to have more copies of this card and replace other Fusion Substitute monsters.
Don't destroy his monsters so he won't deck out faster than you.
I'm farming this currently with Elements unite vassal deck. I only added 2 Sanguine Swamps. Just summon gate guardian in defence an make sure you have a sanguine swamp ready for lasr turn and no other spells/traps when you activate it. This might alo work with jaden. It's super easy and should be doable by anyone once para bros come to the gate permanently