Yakkey

"Heeeeeeelp! Master Tubba Blubbaaaa!! A thieeeeeeef!!!"

- Yakkey

Yakkey (referred to as Mystical Key as an item) is a talking key in Paper Mario. Yakkey's name is a portmanteau of "yak", which means to talk non-stop, and "key". It is needed to open the door to Windy Mill. The key is locked away in a treasure chest in Tubba Blubba's bedroom.

Mario has to sneak past Tubba Blubba, who is sound asleep in his bed, and open the treasure chest containing Yakkey. However, being a talking key who is completely loyal to Tubba Blubba, Yakkey screams out loud to wake its master, after which Mario's active party member will remark about Tubba Blubba waking up and convince Mario into escaping:
 * Goombario: "Tubba Blubba's waking up! Let's get outta here!"
 * Kooper: "Oh-oh. We're in trouble! Tubba Blubba woke up! Let's go!"
 * Bombette: "Tubba Blubba's up! Let's get away!"
 * Parakarry: "Marioooo! Acckk! Tubba Blubba woke up! We'll never make it if we stay here! Run! Run!"
 * Lady Bow: "Oh no, he's awake! We have to run!"

The key can then be used to open the Windy Mill when Mario arrives. Later in the game, Yakkey can be found by the well in the Windy Mill desiring to guard a new secret, hopefully a happy secret such as a present.

Tattle
Goombario can use Tattle on Yakkey when Mario finds it by the well inside Windy Mill.
 * This is Yakkey, a magical key. It was lucky for us that it spilled the beans about Tubba Blubba's secret. But I wonder what it's going to do...