It's possible you're thinking of Rockruff, a Rock-type Pokémon that evolves into Lycanroc.
To catch Rockruff in Pokémon Black, you'll need to find it in the wild. It can be found in several locations:
* Floccesy Ranch: This is the most common place to find Rockruff. It appears during the day.
* Pinwheel Forest: You can find Rockruff here after obtaining the National Pokédex. It appears during the day.
* Undella Bay: Rockruff appears here after obtaining the National Pokédex. It appears during the day.
Remember that you need to be careful when catching Rockruff, as it's a relatively rare Pokémon.
If you're looking for a different Pokémon, please let me know, and I'll try my best to help!