Yawn

Yawn is Slowpoke's specialty. Despite the sleepy name, it's a diagnostic tool: talk to a Yawning Slowpoke and they'll tell you the current humidity level of whichever biome they're in.

Humidity directly affects the comfort level of many Pokémon — some species only want to live in your town if the moisture is just right.

Paired with Water (to raise humidity via Rain Dance) and Burn (to lower it via Sunny Day), Yawn closes the loop, letting you measure and then actively dial in the perfect climate for each habitat.