The Paradox Brothers are obtainable through the event "Paradox Brothers: Guardian of the Gate!" which works similarly to the other Legendary Duelist character unlock events. The event's first appearance is May 24 -31.
Para and Dox, are brothers who duel in a tag team format that worked as eliminators. They were hired by Maximillion Pegasus in the Duelist Kingdom tournament, and ended up dueling against Yugi and his companion. It was also the first tag team duel in the anime/manga.
How to get
Elements Unite! You will start the duel with 500 Life Points and your starting hand will be 1 card, which is "Gate Guardian". In addition, you will start the Duel with Suijin, Kazejin, and Sanga of the Thunder on the side of your field. Their effects are negated and they cannot attack as long as they are face-up on the field.
Restart Can be used after starting hand is distributed. Shuffle all the cards from your hand into the Deck. Then draw the starting hand again
Thunder, Water, and Wind Can be used when you life pints decrease by 1800. Randomly add one "Sanga" "Kazejin" or "Suijin" to your hand (these cards are not drawn from your deck). Can only be used once per duel
Three-Star Demotion Can be used by paying 3000 Life Points. Until the End Phase, reduce the Level of all monsters in your hand by 3. This skill can only be used once per turn.
Labyrinth Builder Shuffle 2 cards from your hand into the Deck to create "Labyrinth Wall" on your side of the field. This skill can only be used once per Duel.
Guardian Call Can be used when your Life Points decrease by 1800. Randomly add 1 "Guardian" card from your Deck to your hand. This skill can only be used once per Duel.
My god these guys are amazing to farm keys/normals in the duel world! Just equip Elements Unite! And bring 3 Fairy Meteor Crush, 3 Inaba White Rabbits, As many Shallow Grave cards you can and nothing but healing cards for the rest. Supremacy Berry, Cure Master, Soul of the Pure, Goblin Thief, Enchanted Javelin etc. The AI can use this very well. We use the rabbits because the AI gets you killed with anything else at low life and the chip is great on a stall or a quick win. Fairy Meteor stops defence stalling and shallow grave will bring back Gate Guardian if he is destroyed or summon back Kazejin, Sanga or Suijin who can now attack. The healing stops you dying to effect damage. Quite often this achieves Quick Victory, No damage, Low Life and Comeback Victory or Destroy X Monsters for 3k score. It's also a godsend for stage 57s win 40 comebacks!
Sorry for the late reply. I'm going to replace the Javelins with Shallow Grave when I get two more. The AI sometimes refuses to use Fairy Crush if your opponents life is low so you might want to take over if this happens though the rabbit will eventually break through
I'm using Unhappy Girl deck with some heal cards, Aegis Gaia and Nutrient Z. The idea is stall using Girl and get u'r LP to more than 6300 as soon as possible then finish w/ Vassal or Piranha combo. Use LP Boost alpha if unlocked for more consistency. Got 7k+ DA.