NEW YORK — The thing that helped college senior Reid Borsak get over playing a lot of video games arrived in the mail by surprise one day.

It was a tarot card — a death tarot card. And it made him realize there was something he could like even more than video games: alternate-reality games.

"It freaked me out for a little while, but then it occurred to me what it was from," he said in an interview last month. "I was pretty much hooked after that."

What Borsak was getting hooked on was a game called "Chasing the Wish." That game, like the rest of the titles in the young genre of alternate-reality games, or ARGs, was an adventure designed to be played in the real world. ARGs aren't played on PlayStations and don't take place exclusively on computer screens. They commonly play out by enmeshing gamers into networks of fake Web sites and tantalizing them with mysterious breaches into the real world, like strange text messages, suspicious phone calls and the occasional mystery package that shows up to further the mystery.

ARGs have been bubbling up for about half a decade but have not yet become mainstream. While some doubt that they can, Borsak's current favorite "Perplex City," an ARG that launched in the U.S. this year, is making a play to be the first.

"These are the really early days for alternate-reality games," said Michael Smith, CEO of "Perplex City" developer Mind Candy, which claims the game has 20,000 registered players worldwide. "But I think it's close to tipping."

Many ARG aficionados consider "The Beast," a game used to build hype for the 2001 movie "A.I.," the first significant effort in the genre. "The Beast" sent players down the proverbial rabbit hole with clues hidden in movie posters and trailers before bringing them into an interweaving complex of Web sites and a story line that had plenty of the not-so-real people on those sites discussing a mysterious murder.

" 'The Beast' was amazingly cool because the developers behind it never came out and talked about it while it was running," Smith said. "That did make the whole experience more exciting, engaging and real for the players."

The game had come unannounced. There had been no release date. Movie fans interested in "A.I." simply started noticing odd things and, by doing some digging and teaming up with each other through the Internet, suddenly found themselves playing a game. That inspired community began creating its own ARGs and looking for more. It's still a matter of debate on sites like the Alternate Reality Gaming Network (ARGN.com) as to whether the latest weird thing on the Web is actually the beginning of a new game format.

Like a more traditional form of advertising, it didn't cost any money to experience "The Beast" — the game was free to all players. That, too, set a trend. Three of the most prominent ARGs of the last two years — "ilovebees," "Last Call Poker" and "The Art of the Heist" — were produced to hype "Halo 2," the video game Western "Gun" and Audi cars, respectively.

Last year in England, Smith and a team of 13 other designers and artists created "Perplex City" as an ARG designed to actually hype itself. The game involves collecting oversize trading cards that feature mazes, word puzzles and optical illusions but also clues — sometimes hidden with ultraviolet or heat-sensitive ink — that tease a deeper story. That tale involves a city in an alternate dimension and that city's lost treasure, which has arrived here on Earth. Somewhere in the real world, Smith's team has buried that treasure and will award $200,000 to the first player who follows the clues and tracks it down.

While the sale of the cards keeps "Perplex City" from having to be a commercial for a sponsoring product, it still resembles "The Beast" in that it involves a network of convincing but fake Web sites — along with a host of other intersections with the real world designed to keep players always guessing about what's real and what's not. One chain of puzzles had players in New York finding a business card that led to Web sites, which in turn led to fake band posters in London, which in turn led to a clue-laden movie trailer playing in London, which then even led to a hint that was delivered from a plane that flew over Manchester, England, with a secret message in tow.

The majority of the game is played through fake Web sites, and, like "The Beast," the designers' intent is to make the mysteries hard to crack. But no matter how obscure they try to be, Smith acknowledges that the hive mind of an international community of ARG players makes it tough to pull one over.

"I think about 98 percent of the puzzles that we've released on the cards have been solved," he said. But there is an exception. "One is a very complex piece of cryptography that we've calculated would take about 30,000 computers running in tandem several months to solve. They haven't managed to get that one yet."

As alluring as the chain of mysteries might be, they aren't without their pitfalls. The first ARG Reid Borsak ever played, 2001's "Majestic," failed to catch on even though it was backed by the mighty Electronic Arts. Gamers weren't interested in paying a monthly fee for one thing, and after September 11, the title proved too unsettling to keep around. "[The game] was quite controversial because of the fact that they would call you up and scare you," Borsak said.

Game designer Frank Lantz, who runs a company called Area/Code that also makes games staged in the real world, said that the puzzle-based nature of many ARGs may wind up hindering widespread popularity.

"There's a very narrow sweet spot for puzzle design where it is challenging, entertaining and rewarding, but not just frustrating," he said.

But Lantz says ARGs still have great potential. Rockers AFI have even entangled their fans in an elaborate online treasure hunt tying in with the release of their next album (see "AFI Fans Surfing, Phoning, Traveling In Cryptic Treasure Hunt"). And Lantz recalled playing an ARG and stumbling across a site of poems that seemed to contain important clues. The site looked real, but Lantz saw some clues that seemed to tie into the game. But maybe, he thought, it was just an ordinary poetry site with no hidden messages.

"I think it was the exact quality, the exact state of mind that ARGs are trying to conjure up: the sense of not knowing, of planting the seed of uncertainty that shifts your perspective on everything you're looking at in the world. You start to see patterns and become sensitive to these kinds of vibrations that you're not normally aware of and that maybe aren't even there." It turned out that the poems Lantz thought he saw clues in weren't even part of the game.

Now Michael Smith hopes gamers will be equally eager to be so mystified with "Perplex City." A third wave of "Perplex City" puzzle cards will be released this month. For more on the game, go to PerplexCity.com.