Sleepy Pharaoh

Taking a look at this, we can see a little bit of Dark Yuugi’s immediate M.O.

Ushio is objectively much bigger and stronger than Yuugi, and he has a weapon. He was just shown to beat Yuugi, as well as his friends. 

Dark Yuugi, immediately, establishes the way he plays games after this.

He immediately takes control of the situation, putting his opponent off of their ideas. He shows initiative in order to be the one in control.

He then puts on an air of bravado, in order to put his opponent on the backfoot, usually by being intimidating, if not downright scary. His confidence, as well as his initiative, are for intimidation. In a physically small form, this is his first line of defense, and a weapon.

Once that is established, he raises the stakes, in order to both entice and frighten his opponent. In this case, he doubles the money, and levels the playing field to something both can physically do--a game. 

It’s been compared to Jigsaw a lot, but what Dark Yuugi is doing here is setting up a way that he can physically be put on a level field with Ushio, following Yuugi’s fears of the fact that he can “never reach Ushio in a hundred years.” He knows that Ushio would physically hurt him, so what he can do here is bet what Ushio wants--money--in a way where he can get out of this without getting hurt.

Ushio is already showing signs of the pressure Dark Yuugi is putting him under. Dark Yuugi also directly calls out the weapon that Ushio is hiding, making a blind prediction off of what Ushio showed him earlier. The way Ushio’s sentences start trailing off show he’s already starting to fall into the pressure of the mind game Dark Yuugi has started.

All of this before the Dark Game has even started--Dark Yuugi has already won.

His heartbeat is starting to race, and he’s sweating. Dark Yuugi doesn’t want him to quit, because then he’ll be a problem for later, so he feeds into Ushio’s ego and what he wants. The 400k yen.

Dark Yuugi is pressing hard--the unnerving confidence is starting to shake Ushio even deeper. He knows exactly what he’s doing.

This, however, is Zorc.

After all, the Penalty Game opens the Door to Darkness, and the first page established the Shadow Games as ritual games of fate. The 3k years of being without an identity has led him to absorb Zorc’s being into a replacement of that identity, until Yuugi provided him another identity to become.

It’s also notable that Dark Yuugi doesn’t use magic at all. This game is played completely fairly. (Also nice detail that he won the sham-bo.)

He also keeps up conversation, and usually leads his opponent to believe they’ve gotten the upper hand, before a weakness is revealed. It’s also notable that his strength is adaptability. Here he freely admits he genuinely was surprised, since these games are usually off-hand and made up on the spot. (Usually, his opponent’s own arrogance does them in, though in this case it’s greed instead of arrogance.)

The mind game is most of the game. Ushio is already cracking before he even makes his first move.

And here we come to the point where Dark Yuugi goes in for the kill.

Throughout the entire game, Ushio has had so much pressure put on him that he’s starting to crack. Dark Yuugi lays it in--going in for the final piece that will make Ushio crack.

Now, we know from later on that this isn’t the case. Dark Bakura flat out cheats several times. Dark Yuugi is presenting Ushio no option of winning, which pushes Ushio to cheat first, since Dark Yuugi has gotten so into his head that he sees no other option. (It's also worth noting that Dark Yuugi and Kaiba later express that a person's true nature is in how they play games, so it's very likely he personally believes it, but it has nothing to do with the magic of the Dark Game.)

And this is the moment Ushio breaks the rules, because he sincerely believes Dark Yuugi's bluffs.