Just build a deck with 10 cards with 1200+ ATK and 10 cards with 500 ATK. First play a 1200+ ATK monster and then attack his monsters (preferably the 1000 ATK monster) with your 500ATK monsters until you're at 500. I took one extra swing at his 850 ATK monster since I wasn't sure what LP the comeback victory kicks in at.
Hey! Here's a link to a video of me achieving a comeback victory with Enemy Controller, a common card that's easy to obtain
your LP must be lower than your opponent at the start of the turn that u win