What does the Sassy nature do?

Sassy raises Sp. Def by 10% and lowers Speed by 10%.

What stat does Sassy increase?

Sassy increases Sp. Def by 10% and decreases Speed by 10%. HP is unaffected.

A Sassy Pokémon likes Bitter flavors (tied to Sp. Def) and dislikes Sweet flavors (tied to Speed).

Yes. Use a Sassy Mint to apply the Sassy stat effect to any Pokémon without changing its displayed nature.

Nature

Raises Sp. Def, lowers Speed.

Raises Sp. Def +10%

Lowers Speed −10%

LikesBitter

DislikesSweet

Slow special walls, Trick Room special tanks.

Calm −Attack Gentle −Defense Careful −Sp. Atk

What does the Sassy nature do?: Sassy raises Sp. Def by 10% and lowers Speed by 10%.
What stat does Sassy increase?: Sassy increases Sp. Def by 10% and decreases Speed by 10%. HP is unaffected.
What flavor does a Sassy Pokémon like?: A Sassy Pokémon likes Bitter flavors (tied to Sp. Def) and dislikes Sweet flavors (tied to Speed).
Can I change a Pokémon to Sassy?: Yes. Use a Sassy Mint to apply the Sassy stat effect to any Pokémon without changing its displayed nature.