Yu - Gi - Oh ! - Episode 021 " Double Trouble Duel , Part 3 " , known as " Demon Dragon ! Black Demons Dragon " in the Japanese version , is the twenty - first episode of the " Yu - Gi - Oh ! " second series anime . It first aired in Japan on September 12 , 2000 and in the United States on March 30 , 2002 . Summary . Joey Summon s " Red - Eyes Black Dragon " and Yugi activates " Polymerization " to form " Black Skull Dragon " by fusing " Red - Eyes Black Dragon " with " Summoned Skull . This monster helps them win the duel even with the no - flying zone rule mentioned by the brothers . Yugi and Joey now have 10 Star Chip s each . However , they must still choose one of the brothers ' doors , and Yugi still does not trust either brother . He has correctly guessed that the brothers can alter the real - life labyrinth , ensuring that whichever door their enemies choose does not lead to freedom . However , Yugi does not mention this realization right away . He holds up two coins , each of which bears the emblem of Para or of Dox . He holds them in his fists , saying he will open one hand , and the concealed coin will be the chosen door . He opens one hand , and when the brothers see the Dox mark , they accept his apparent selection of the Para door . Then they smile and reveal that the Dox door was correct all along . At this point , Yugi reveals their secret , and he opens his other hand , showing the Dox coin . The first coin had been marked with one emblem on each side . Because the brothers fell into their own trap - a hand that can tell lies - the friends are free . Down in Pegasus ' s dungeon , Seto Kaiba finds Mokuba , but is soon confronted by Pegasus , who uses his Millennium Eye to lock Mokuba ' s soul in a card . He tells Kaiba that if he wants to see Mokuba again , he must defeat Yugi . Featured Duel : Yami Yugi & Joey Wheeler vs . Para & Dox . Yugi has 800 LP remaining , and control s " Dark Magician " ( 2500 / 2100 ) in Attack Position hidden under " Magical Hats " and 2 Set cards . Joey has 1600 LP remaining , and controls " Flame Swordsman " ( 2500 / 1600 ) in Attack Position equip ped with " Salamandra " and no Set cards . Para has 1700 LP remaining , and controls " Sanga of the Thunder " ( 2600 / 2200 ) and " Monster Tamer " ( 1800 / 1600 ) both in Attack Position and no Set cards . Dox has 1600 LP remaining , and controls " Suijin " ( 2500 / 2400 ) and " Kazejin " ( 2400 / 2200 ) both in Attack Position , combined with " Kazejin " as " Gate Guardian " , " Labyrinth Wall " and no Set cards . Turn 23 : Para " Sanga of the Thunder " attack s " Flame Swordsman " , but Yugi activate s his face - down " Mirror Force " to reflect the attack back at Para ' s and Dox ' s monster s . Para activates the effect of " Kazejin " to reduce the battle damage to " Gate Guardian " to 0 , but the reflected attack still destroy s " Monster Tamer " , and Para receives damage equal to the difference between the ATK of the attacking " Sanga of the Thunder " and the destroyed " Monster Tamer " ( Para : 1700 → 900 LP ) . Turn 24 : Joey " Flame Swordsman " attacks " Kazejin " , but Dox activates the effect of " Suijin " to reduce the battle damage to 0 . Turn 25 : Dox " Suijin " attacks " Flame Swordsman " . Visually , the attack literally ' floods ' the maze with water , sweeping everything in its path . " Dark Magician " is protected by " Magical Hats " , but since " Flame Swordsman " is weak against water attacks , it loses 300 ATK ( " Flame Swordsman " : 2500 → 2200 / 1600 ) . " Suijin " destroys " Flame Swordsman " ( Joey : 1600 → 1300 LP ) . Turn 26 : Yami Yugi Yugi draw s . He then Sets a card and Normal Summon s " Summoned Skull " ( 2500 / 1200 ) in Attack Position . Using the trail of water left by " Suijin ' s " attack , " Summoned Skull " electrically attacks " Suijin " without being adjacent to it . Dox tries to activate the effect of " Kazejin " to reduce the battle damage to 0 , but Yugi activates his face - down " Spellbinding Circle " , which prevents the sections of " Gate Guardian " from activating their effects , attacking or changing their battle position s , and decreases their ATK by 700 ( " Sanga of the Thunder " : 2600 → 1900 / 2200 , " Kazejin " : 2400 → 1700 / 2200 , " Suijin " : 2500 → 1800 / 2400 ) . " Summoned Skull " destroys " Suijin " ( Dox : 1600 → 900 LP ) . Turn 27 : Para Para activates " Remove Trap " to destroy " Spellbinding Circle " ( " Sanga of the Thunder " : 1900 → 2600 / 2200 , " Kazejin " : 1700 → 2400 / 2200 ) . Turn 28 : Joey Joey draws " Red - Eyes Black Dragon " and subsequently Normal Summon s it ( 2400 / 2000 ) in Attack Position . Yugi then activates " Polymerization " to fuse " Summoned Skull " with " Red - Eyes Black Dragon " and Fusion Summon " Black Skull Dragon " ( 3200 / 2500 ) in Attack Position . The Paradox Brothers then mention a special rule : the Labyrinth is a no - flying zone ( i . e . flying monsters cannot move through it ) , therefore " Black Skull Dragon " is unable to move any spaces . Turn 29 : Dox Dox draws " Riryoku " and subsequently activates it to halve Yugi ' s and Joey ' s Life Points ( Yugi : 800 → 400 LP , Joey : 1300 → 650 LP ) and add them to the ATK of " Gate Guardian ' s " remaining parts ( " Sanga of the Thunder " : 2600 → 3000 / 2200 , " Kazejin " : 2400 → 3050 / 2200 ) . Because he activated " Riryoku " , Dox must end his turn . Turn 30 : Yami Yugi Yugi draws . He then releases " Dark Magician " from the " Hat " it was under , then moves it to the end of the labyrinth , right in front of " Gate Guardian " . He then activates " Reborn the Monster " to Special Summon " Suijin " ( 2500 / 2400 ) from Dox ' s Graveyard to his side of the field in Defense Position . Turn 31 : Para Para begins his turn without waiting to find out what monster Yugi revived . " Gate Guardian " attacks " Dark Magician " , but Yugi activates the effect of " Suijin " to reduce the battle damage to 0 . Turn 32 : Joey Joey draws " Copycat " and subsequently activates it as a Spell Card . He then uses the effect of " Copycat " to activate the effect of " Riryoku " as its effect , halving the Paradox Brothers ' Life Points ( Para : 900 → 450 LP , Dox : 900 → 450 LP ) and adding them to the ATK of " Black Skull Dragon " ( " Black Skull Dragon " : 3200 → 4100 / 2500 ) ( NOTE : In the anime , Black Skull Dragon ' s ATK only went up to 4000 ) . Turn 33 : Dox " Kazejin " attacks " Suijin " , but Yugi activates the effect of " Suijin " to reduce the battle damage to 0 . " Sanga of the Thunder " attacks and destroys " Suijin " ( as the effect of " Suijin " can only be used once per turn ) . Turn 34 : Yami Yugi Yugi activates his face - down " Monster Replace " to make " Dark Magician " and " Black Skull Dragon " switch locations . " Black Skull Dragon " attacks and destroys " Gate Guardian " ( Para : 450 → 0 LP , Dox : 450 → 0 LP ) . Aftermath . Yugi and Joey win , obtaining the necessary ten Star Chip s needed to enter Pegasus Castle . Yugi then uses two marked coins to select Dox ' s door while ensuring that it is the correct one to lead him and his friends out of the maze . Featured cards . The following cards appeared in this episode . Cards in italics debuted here .