Pokémon Sleep has announced that Happiny, Chansey, and Blissey will be joining the game starting on May 5th, 2025.

New Arrivals: Happiny, Chansey, and Blissey

There have been reports of Pokémon appearing that we haven’t seen around here before—maybe this is thanks to the sleep research you’ve all been conducting! It may be possible to encounter them during sleep research sometime soon.

New Arrivals
• Happiny – Normal
• Chansey – Normal
• Blissey – Normal

We hope you’re looking forward to this!

Newly Arriving Pokémon Details

Appearing Beginning: May. 5, 2025, at 3:00 p.m.
Note: Pokémon Incense for the new arrivals can be used starting from the date and time above.

Appearing at: Greengrass Isle, Cyan Beach, and Snowdrop Tundra
Sleep Types:
Happiny: Slumbering
Chansey: Snoozing
Blissey: Snoozing

Source: https://www.pokemonsleep.net/en/news/323539313431353733313531383137373239/