Niantic Labs has announced that a handful of new Pokémon from Gold and Silver's second generation have arrived in its hit mobile game Pokémon Go. Players will have to visit PokéStops to collect Pokémon eggs that may hatch baby critters such as Pichu, Togepi and Igglybuff. The team also announced that players would now be able to hunt for a new limited edition Pikachu adorned with a festive Santa hat to celebrate the holiday season.

"Trainers will have the opportunity to hatch these and several other Pokémon that were originally discovered in the Johto Region in Pokémon Gold and Pokémon Silver video games," the developer wrote in a blog post, noting that more pocket monsters will be released over the coming months.

However, fans have already voiced their disappointment in the update that many expected would release all 100 Gen 2 pocket monsters. Last month,data miners at The Silph Road found code for the entire second generation roster of Pokémon including mentions of Celebi, Chikorita, Totodile among others.

"This was the big announce?" one commenter wrote on the developer's announcement post on Facebook. "What about the second generation? And the legendary Pokemon? And the trades? And the battles? Very bad, Niantic."

Another wrote: "Your game is dying. I love to play and explore with Pokémon Go. But this type of slow response is killing it. I hope there is more in store because the excitement for many."

However, some fans defended the developer's decision saying a slow but continuous release of new creatures would keep players coming back for more.

On Reddit and Twitter, players have already reported hatching Magby, Elekid, Igglybuff and Smoochum among others in the game thus far.

Regarding the limited edition Pikachu, excited players have already begun posting their captures of the series' mascot on social media.

Niantic said players should not have trouble finding the beloved holiday-themed Pikachu in the wild as "large quantities" of the little critter will pop up until the event ends on 29 December.

"As we race toward 2017, we can't help but feel grateful for the support and reaction to the Pokémon Go community has given us, and we're delighted to start rolling out select Pokémon for them to hatch," Niantic product director Kei Kawai said in a statement.

"We're also looking forward to celebrating the season with our community by introducing a Pikachu wearing a festive hat, providing Trainers the opportunity to get out and explore their neighborhoods with friends and family as they gather for the holidays."

Following its successful release in July, the mobile game quickly mushroomed into a global phenomenon that saw millions of players from around the world venturing outside to find and capture the beloved pocket monsters via the GPS-powered game.

The latest update comes as Niantic attempts to revive interest and coax players back to its popular game following the initial Pokémania over the summer that seems to have dissipated in recent months.

The developer recently unveiled a series of announcements including turning thousands of Sprint and Starbucks stores into PokéStops and Gyms, a new berry-filled, Pokémon-themed Starbucks Frappuccino, limited-time holiday events and regular updates. It also expanded the Pokémon Go's Nearby feature again to include "most" regions around the world.

Last week's update included the ability to transfer multiple Pokémon at a time and made a few changes to the game's buddy system.

Pokémon Go is available now for Android and iOS.