After his loss to Yuya Sakaki, Sawatari is out for revenge with his new cards. Overhearing this, Yuzu decides to take matters in her own hands and duel him, but she is upstaged by a mysterious masked duelist, who Sylvio dubs "The Dark Duelist (Mr. Mystery)".
Initially, the Dark Duelist seems to be on the back foot against Sawatari's new Monarchs, until he reveals that he can Xyz Summon, which is revealed to be a Summon that only high-level LDS students can learn about. With that, he brings out his ace monster, Dark Rebellion Xyz Dragon, and proceeds to wreck Sawatari's monsters, ask about Academia (Duel Academy), and nearly skewer him with a spear from one of his spell cards. He also demonstrates an ability to make the impacts in a duel real...despite it not being an Action Field.
After winning, the Duelist unmasks himself, revealing that he has the same face as Yuya, but he vanishes in a bright light just as the real Yuya shows up.
This episode contains examples of:
- Absurdly High-Stakes Game: This episode reintroduces the power to make duel impacts real. The high stakes are subverted by the Duelist though, as later episodes reveal that losers of such duels are sealed into cards.
- Black Knight: The Phantom Knights of Shadow Veil, and the eponymous duelist himself.
- Cerebus Syndrome: This episode is somewhat darker than the others, and served as the tip of the spear (pun fully intended) for the main story arc.
- Crazy-Prepared: Sawatari, so much so that his move bordered on outright paranoia: He set Ice Rage just in case the mystery duelist defeated Mobius, despite neither knowing that monster used to do so existed nor believing that his opponent was a skilled enough duelist to summon it (as evidenced by his Underestimating Badassery). Despite this, he was still ready for the possibility. Unfortunately for him, his opponent was still a little more prepared.
- Curb-Stomp Battle: Sawatari wasn't doing too badly, clearing all five of Mystery's back row in a single turn and summoning Mobius The Mega Monarch to boot, but Mystery utterly flattened him.
- Evil Counterpart: The Dark Duelist appears to be one to Yuya.
- Impaled with Extreme Prejudice: Subverted. The "Phantom Spear (Phantom Des Spear)" only pierced Sawatari's jacket, though the imagery involved fools us for a bit.
- I Take Offense to That Last One!: Being called a coward and a sore-loser? It's being called a second-rate duelist that pisses Sawatari off. Yuzu takes note of this, lowering it to hundred-rate. In the dub, he doesn't mind being called chicken, but takes offense to being reminded of his defeat to Yuya.
- No Name Given: Mr. Mystery is the name Sawatari uses to refer to him in dub, while "The Dark Duelist" is a moniker given by the Japanese production staff, and is read as "Unknown" by the Versus Character Splash. His true name is later revealed as Yuto.
- "The Reason You Suck" Speech: The Dark Duelist gives this to Sawatari.
- Shock and Awe: Dark Rebellion Xyz Dragon's preferred method of attack, despite its name.
- Underestimating Badassery: Sawatari falls prey to this, thinking that a tough guy like his opponent can't be so tough if he can't summon a monster. He is horrifically proven wrong when the Dark Duelist not only OTKs him, but is able to do so precisely because Sawatari destroyed his back row.
- Wham Episode: The duelist is revealed to look like Yuya, and is mistaken as such by Yuzu (who appears to have some connection to the guy, and her bracelet acts strange as well), kicking off the Best-of-Three mini-arc. This is also the first mention of apparent Greater-Scope Villain Duel Academy.