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 use this deck with cyber blader to farm bastion lv40. 100% farm sucess rate. Summon gate gaurdian in defence mode keep drawing and last turn summon cyber blader and vassal.
Cyber blader' s effect negates all his cards effects while he has 3 monsters on his side of the field so dont destroy his monsters.
You also need 1 fusion twin headed thunder dragon. 1st turn summon Gate guardian on defense Mode. Draw all your deck and on last turn summon Vassal,activate Treasure pass and both unions,change Gate guardian to atk and fusion thunder dragon.Go to Battle step and activate antimagic arrows and direct attack.Ez 8k
If you don't have Anti-Magic Arrows, but have unlocked Alexis, you can let the opponent swarm the field, then Summon Cyber Blader at the last turn. Cyber Blader negates all of the opponent's effects if they have 3 monsters.