Most of you know that to get a hidden ability you have to catch the Pokemon in the horde with the ability or in the friend safari. I checked bulbapedia and there is no way to get a horde encounter with a group of Qwilfish or in the friend safari. it is impossible to get it a hidden ability in a wild Pokemon to my understanding so how can someone get a Qwilfish with the hidden ability?
Thanks for the help!
For a HA qwilish you will need to transfer from older version.
Source:http://www.serebii.net/pokedex-xy/211.shtml
Hope I helped :D
I know this is old, but you can also now use the virtual player versions of GSC which defaults to the hidden ability when transferred.
You can get a HA Qwilfish in Sword/Shield. Qwilfish has a chance to spawn in these raid dens:
You can find Qwilfish raids in the following locations: Bridge Field, Dusty Bowl, East Lake Axewell, Giant's Cap, Hammerlocke Hills, Lake of Outrage, Motostoke Riverbank, North Lake Miloch, South Lake Miloch, West Lake Axewell.
If the den is 4 or 5 stars, then there is a chance Qwilfish will have it's HA. I cannot find a clear percentage on the chance of a Pokemon having it's HA in a max raid battle, unfortunately. (Most sites say around 20-30% in 4-5 star Max Raid dens.) On the bright side, you'll know if Qwilfish has it's HA immediately.
Source for Quote Which Pokemon can have their HA in a Raid Den