Sassy Nature

Sassy raises Sp. Defense by 10% and lowers Speed by 10%. At level 100 with full investment, that's roughly a 30-point swing on the boosted stat. Pokemon with Sassy nature prefer Bitter flavor and dislike Sweet.

Top Sassy users include Ting-Lu, Amoonguss, Farigiraf, and Aegislash. They benefit from the Sp. Defense boost because their main damage comes from that stat. The Speed drop doesn't hurt them since they don't rely on it.

Sassy is a strong competitive nature. The -Speed drop actually helps under Trick Room, where slower Pokemon move first. The key is matching it to Pokemon that don't need Speed in their moveset.

Synchronize is the fastest method. Lead with a Pokemon that has Synchronize and Sassy nature, and wild encounters match it (Gen 3+). Breeding works too: give the Sassy parent an Everstone and all offspring inherit the nature. Nature Mints (Gen 8+) let you change the stat effect to Sassy without rebreeding.

Sassy prioritizes Trick Room special wall, while Calm goes for standard special wall. Pick Sassy when your Pokemon's role depends on the stat it boosts. Go with Calm when standard special wall matters more for your team.