6 species have Own Tempo as a hidden ability, 22 as a normal one

Effect, in PokéAPI's words

“Prevents confusion.”

As a hidden ability

Species	Slot	Note
Lotad	Hidden	Since Generation V
Lombre	Hidden	Since Generation V
Ludicolo	Hidden	Since Generation V
Numel	Hidden	Since Generation V
Espurr	Hidden
Tandemaus	Hidden

As a normal ability

Species	Slot	Note
Slowpoke	Normal
Slowbro	Normal
Lickitung	Normal
Slowking	Normal
Smeargle	Normal
Spoink	Normal
Grumpig	Normal
Spinda	Normal
Glameow	Normal
Purugly	Normal
Lickilicky	Normal
Petilil	Normal
Lilligant	Normal
Bergmite	Normal
Avalugg	Normal
Mudbray	Normal
Mudsdale	Normal
Fidough	Normal
Tadbulb	Normal
Tinkatink	Normal
Tinkatuff	Normal
Tinkaton	Normal

Elsewhere in PokéAPI

5 more holders without a page here

Alternate forms and other species that PokéAPI lists with Own Tempo.

Rockruff Own Tempo, Slowpoke Galar, Slowbro Galar, Slowking Galar, Indeedee Female