On their screens, players of the viral mobile game “Pokémon Go” are seeing these creatures pop into existence alongside real-world physical objects. The mole-like Diglett peeks out of a toilet. A flaming demon Shetland called Ponyta gallops across the National Mall. A ostrich-like Doduo appears on top of the hold button of an office phone.

Capturing these little monsters isn’t just good for players. In just a few days since its July 6 launch, the game has become a national sensation, nearly overtaking Twitter in daily active users. It currently ranks as the most profitable game on Google and Apple’s app stores. On Monday, Nintendo’s stock jumped 25 percent. On Tuesday, it rose another 13 percent.

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The game is perhaps the first real success story of the use of augmented reality technology, which blends the digital and real world together. The combined effect is part bird-watching, part geocaching, part trophy-hunting, with a heavy dose of mid-1990s nostalgia.

All that success means Pokémon Go won’t be the last of these types of games.

“It’ll get bigger before it gets smaller,” said Michael Pachter, a gaming analyst for Wedbush Securities. “I just hope that nobody actually gets killed walking into traffic.”

Indeed, not everyone has just found animated monsters through the game. Some caught trouble.

In Riverton, Wyo., 19-year-old Shayla Wiggins was looking for Pokémon along the banks of the Wind River when she found a real body in the water. Missouri police reported that four people used the game to lure victims to isolated areas and rob them.

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One player said the game “put me in the ER.”

“Not even 30 minutes after the release last night, I slipped and fell down a ditch,” wrote a Reddit user (Yes, the game already has its own section of Reddit). “Fractured the fifth metatarsal bone in my foot, 6-8 weeks for recovery. I told all the doctors I was walking my dog. . . . Watch where you’re going, folks!”

For the uninitiated, Pokémon Go invites players to hunt for digital Pokémon on their smartphones. The catch is that the game, unlike the original Nintendo series and most video games, requires physical exploration in the real world. The critters are placed using GPS and an algorithm by Niantic Labs, a software and gaming company.

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To collect Pokémon, players walk to a location and spy them on their smartphone. With an upward flick of a finger or thumb, as though playing the world’s tiniest game of skee ball, the Pokémon Go player attempts to capture these creatures with Pokéballs. Repeated captures of the same type of creature yield candies. Feeding enough candies to a Pokémon causes it to grow in power. Powerful creatures battle at gyms, which are digital arenas located at real points of interest.

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One of them is the fountain on the White House’s North Lawn. (Players must stand on the civilian side of the fence, of course.)

Perhaps the only bad news this week for the game’s developers is that the app’s immense popularity is crashing servers. The game frequently freezes. As of Monday, it was still difficult to sign up to become a new player. International rollouts of the game have been delayed while Niantic and the Pokémon Co. figure out how to keep things up and running.

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Undoubtedly, some gaming analysts said, the success of Pokémon Go will inspire clones. Developers are likely being pulled into meeting rooms this week and ordered to make something like this app, said Timothy Carone, a professor at the University of Notre Dame.

“It’s easy enough to duplicate from a technical perspective,” Carone said. Capturing the right user experience, however, is not nearly as easy. There are, after all, few franchises that work as well with augmented reality as Pokémon does.

The game’s real-world interaction just happens to match the premise of the franchise, which features characters journeying from gym to gym as they capture and train adorable monsters that they find in the wild.

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Its makers also have made the game highly shareable. The delight of seeing a little monster pop up on the sidewalk in front of your home, or, in one case, on the bed of your wife while she’s in labor — has been social media gold for players.

The game was a much-needed win for Nintendo, which Pachter, the Wedbush gaming analyst, estimates will make at least $25 million from the app this year, despite not having developed it. The Japanese company is a part-owner of the franchise’s parent company, the Pokémon Co., and had the right to keep Pokémon games exclusively on its own consoles. Still, the fact that Nintendo gave its blessing to the game is a sign that it is loosening its long-held resistance to mobile games. Nintendo has developed three apps so far with a mobile game company, including its Miitomo social network, which was a modest hit when it was released earlier this summer.

But there has been nothing like the success of Pokémon Go. Despite the enthusiasm around the new app, some are not sure how long it will last.

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“It’s a craze,” said Pachter. It may have a long shelf life for a craze, he said — at least as long as it takes most people to catch every Pokémon— but he doesn’t see it lasting forever. “Pet Rocks lasted more than 100 days, too,” he said.