Where to Find and Catch Happiny
From Pokemon Go Wiki
Happiny are found and captured in Nest and Habitat locations.
Nests
Happiny Nests are locations that consistently spawn Happiny.
Habitats
Happiny Habitats are spawn locations where Happiny is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here:
