How to Get Belly Drum in Pokemon Scarlet and Violet

Belly Drum can be learned by a few Pokemon in Scarlet and Violet through leveling up, but the most direct way to get it for others is by using a Mirror Herb. You've gotta find a Pokemon that naturally learns Belly Drum, like Makuhita or Crabrawler, then have your desired Pokemon hold a Mirror Herb while battling alongside the Belly Drum user in a double battle. Once the natural learner uses Belly Drum, your Pokemon will copy it with the Mirror Herb, learning the move permanently. Just make sure your Pokemon is actually capable of learning Belly Drum, not all Pokemon can!

Actually, the Mirror Herb method is overrated. It's way simpler to just evolve a Makuhita into Hariyama who learns Belly Drum at level 40. No need for fancy items or strategies, just good old leveling up.