Where to Find and Catch Mareanie
From Pokemon Go Wiki
Mareanie are found and captured in Nest and Habitat locations.
Nests
Mareanie Nests are locations that consistently spawn Mareanie.
Habitats
Mareanie Habitats are spawn locations where Mareanie 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: