On another searing 90-degree day at Waterfront Park, children splashed their parents in the Pineapple Fountain while a bearded tourist from Connecticut furiously tapped the screen of his smartphone. Beads of sweat pooled on his forehead.

A battle raged between Dennis Berry’s Doduo, a two-headed bird, and an opponent’s Pinsir, a thorned beetle-like bug.

“You’re gonna get your (butt) kicked,” his buddy sneered.

Berry arrived in Charleston on Friday for a friend’s bachelor party. He started playing “Pokemon Go” at Rita’s on Folly Beach on Sunday. His head has been buried in his phone ever since.

“I don’t know really what I’m doing. I’m just playing,” Berry said, an admission that made his friends cackle. “I’m 34. I thought people were losers who did it back then.”

Now Berry has joined their ranks.

“Pokemon Go,” released last week, an augmented reality smartphone game — and now bona fide cultural phenomenon — has uprooted legions of gamers from their summer doldrums and sent them out onto their neighborhood streets, searching for fictional creatures in real-life schools, offices, parks and other city landmarks using GPS technology.

The game’s runaway success has sent Nintendo stocks soaring. “Pokemon Go” is now the top-downloaded app in Apple’s App Store and on track to overtake Twitter in daily active users on Android devices.

The game requires users to leave their homes and hit the streets in search of Pokemon and other items, like potions, revives, incense and egg incubators at real-world Pokestops. (The Post and Courier office is one.) They “catch” Pokemon with Pokeballs and stage battles between other players’ Pokemon at designated sites — such as churches, monuments or restaurants — called “gyms.”

For millennials, the game masterfully exploits their obsession with smartphones and fondness for childhood nostalgia. Nintendo’s Pokemon franchise debuted in 1996, first with a pair of Game Boy games allowing players to catch and train 151 “pocket monsters” and later collectible trading cards, an anime TV series and a roster of feature-length films.

“ ‘Pokemon Go’ is allowing fans of Pokemon to do what the fandom at its core is really about,” said Josh Long, 23, of Goose Creek, who founded the Facebook group “Pokemon Go - South Carolina,” where aspiring Pokemon masters can crow about their gym conquests and post photos of their spoils. The group has amassed more than 200 members and counting since last Wednesday.

“We, like the characters in the game and in the TV show,” Long continued, “can get out in the heat and in the rain and catch (Pokemon).”

As daylight turned into dusk Monday, dozens of players ambled through Marion Square, heads bowed, eyes glued to their phones, flicking their thumbs across their screens in pursuit of Charmanders, Jynxes and Sandshrews. A few settled on blankets in the grass with their phones plugged into the Square’s charging stations.

Brent Dorwart, a 27-year-old theater teacher, laughed when he admitted he was up until 3 or 3:30 a.m. Monday prowling neighborhoods for virtual Pokemon with a flashlight in the suburbs of Goose Creek — a late-night excursion that probably raised a few eyebrows.

Dorwart and his fiance, J.P. Del Valle, 29, a nurse at the Medical University of South Carolina, arrived at Marion Square prepared for a long hunt, each with external battery chargers for iPhones in their pockets. Dorwart carried a 2-liter jug of iced green tea in his backpack “to help with metabolism.”

“I’ve been trying to lose weight. I’ve walked at least 30-40 kilometers in the last few days whereas I didn’t leave the house for exercise at all even in this heat,” Dorwart said. “I know I’m going to keep doing this until I shed at least 50 pounds.”

Cody Robbins, 19, took aim at a flying purple Zubat. After sleeping in Monday, Robbins took the day off work to run errands and search for Pokemon. His older brother got him hooked on the imaginary creatures when he was 5. He played the Game Boy game, collected a tub full of trading cards and took to wearing a red baseball cap like his idol, Ash Ketchum, the character from the Pokemon anime series.

Robbins plans to pass his penchant for Pokemon to his infant son. He even bought him his first Pikachu toy.

“I downloaded (the app) and I just freaked out. My girlfriend was like, ‘You’re stupid,’ ” Robbins said. “She was like, ‘You’re gonna get arrested if you go somewhere you’re not supposed to go trying to get Pokemon,’ and I was like, ‘As long as I get it. Whatever ... I mean, you gotta catch ’em all.”

Alison Graham contributed to this report.

Reach Deanna Pan at 843-937-5764.