Paradox Brothers

The Meikyū Brothers (Paradox Brothers in the English anime) are antagonists in the Yu-Gi-Oh! anime. They are named Mei and Kyū in the Japanese version, and the kanji of their names form the word for labyrinth. Their English names are Para and Dox, and join to form paradox. They are voiced by Wayne Grayson and Marc Thompson in the dub.

History
The Paradox Brothers first appear in a cavern on Duelist Kingdom, hired by Maximillion Pegasus as Duelist Eliminators (Player Killers). They challenge Yugi Mutou and Katsuya Jonouchi (Joey Wheeler) to a special tag-team duel that quickly becomes a maze-like movement game when the Brothers summon Labyrinth Wall. Although they nearly win with their Gate Guardian, Yugi and Joey pool their efforts to create Black Skull Dragon to defeat them.

Afterwards, the Brothers allow them to pass, but warn that there are two paths out of the arena: one leads out of the caves, while another leads to an endless maze. As a way of helping the two, the Brothers claim that one of them will speak only lies, while the other will speak only the truth, and furthermore allow both Yugi and Joey to ask one question each to find out which path is correct. However, Yugi deduces that not only are both brothers lying, but in fact they have the power to change which path leads where. By using a two-headed coin to trick the Brothers into admitting this, Yugi and Joey escape the caves.

The Paradox Brothers also appeared in the Waking the Dragons arc as lost souls wandering the sacred circle Yugi ventures through to find his other half. This would hint that there souls may have been captured by The Seal of Orichalcos, but it is not made clear.

In the Japanese epilogue at the end of the final episode (not seen in the English version), the brothers are seen dueling against Vivian Wong and Mai Valentine on the Great Wall of China.

The brothers also appear in Yu-Gi-Oh! GX as dueling mercenaries that carry their duel against Yugi and Joey as their only loss. Dueling Jaden Yuki and Syrus Truesdale in a duel to determine if the two are expelled from Duel Academy, the Brothers once again call forth Gate Guardian, but allow it to be destroyed to call forth an even more powerful creature, the sinister Dark Guardian, a monster immune to being destroyed in battle. Much like Yugi's duo before them, Jaden and Syrus pool their efforts to create UFOroid Fighter to defeat the brothers.

Voice/Mannerisms
In the 4Kids English dub, they speak with Chinese accents almost exclusively in rhymes, one brother completing the other's sentence. It does not appear that this is present in the original.

In the Japanese version, Mei is voiced by Eiji Takemoto and Kyū is voiced by Hitoshi Nishimura.

In the Singapore English dub, they do not have Chinese accents and do not speak in rhyme.

Deck
In Yu-Gi-Oh!, the Brothers played a Labyrinth Deck of monsters found in dungeons. In Yu-Gi-Oh! GX, they use a Deck focusing on summoning "Gate Guardian".