Equip Junk Barrage to one of your opponent’s monsters. Now, each time that monster destroys a monster by battle and sends it to the Graveyard, your opponent will take damage equal to half the destroyed monster’s ATK in the Graveyard.
Normal Summon Nimble Sunfish or, if you don’t have it in your hand, Mother Grizzly and attack the opponent’s monster that you equipped with Junk Barrage.
When Nimble Sunfish is destroyed by battle and sent to the Graveyard, you will be able to send a Fish-Type monster from your Deck to the Graveyard and then Special Summon another Nimble Sunfish from your Deck. If you send Nimble Angler from your Deck to the Graveyard, it will allow you to Special Summon up to two level 3 or lower “Nimble” monsters from your Deck. Use Angler’s effect to Special Summon two copies of Nimble Musasabi and then Special Summon your second Nimble Sunfish. Now your opponent has lost 500 Life Points and you still have three monsters on your midfield ready to attack.
Attack the opponent’s monster that you equipped with Junk Barrage with both copies of Nimble Musasabi and don’t activate their effect. Nimble Musasabi will deal 500 damage to your opponent via its own effect and 400 additional damage because of Junk barrage. If you are keeping count, you have dealt 2300 damage so far.
Attack your opponent with Nimble Sunfish, send Nimble Angler from your Deck to the Graveyard and Special Summon your last Nimble Musasabi and Sunfish from your Deck. If you now attack with Nimble Musasabi and Nimble Sunfish, you should be able to close the Duel. That’s 4200 damage in a single turn.
If you don’t open with Nimble Sunfish, you can still OTK your opponent as long as you have Mother Grizzly in your hand. Just attack with Mother Grizzly and then use its effect to Special Summon Nimble Sunfish.
Even if your opponent decides not to read what Junk Barrage does, they will quickly understand how the Equip Spell interacts with your “Nimble” monsters. If they have a way of stopping you, they will very likely try and use it. Use Cosmic Cyclone, Hey, Trunade! or any other form of back row removal to get rid of whatever your opponent might have in their Spell & Trap Zones before Summoning your Nimble Sunfish.
Unless the opponent’s monster equipped with Junk Barrage conveniently has less than 1400 ATK, by continuously attacking into it with low ATK monsters, you would definitely go down before you are able to OTK your opponent. Holy Guard is what makes this strategy even remotely viable.