6 species have Competitive as a hidden ability, 7 as a normal one

Effect, in PokéAPI's words

“Raises Special Attack by two stages upon having any stat lowered.”

As a hidden ability

Species	Slot	Note
Piplup	Hidden	Since Generation IX
Prinplup	Hidden	Since Generation V
Empoleon	Hidden	Since Generation V
Boltund	Hidden
Wattrel	Hidden
Kilowattrel	Hidden

As a normal ability

Species	Slot	Note
Jigglypuff	Normal	Since Generation VI
Wigglytuff	Normal	Since Generation VI
Igglybuff	Normal
Milotic	Normal	Since Generation VI
Gothita	Normal
Gothorita	Normal
Gothitelle	Normal

Elsewhere in PokéAPI

2 more holders without a page here

Alternate forms and other species that PokéAPI lists with Competitive.

Meowstic Female (hidden), Articuno Galar