Go to the east-side of Roughport.Slide through the crack in paper-thin mode.Use Flurrie's wind-power and blow the back of the wall.A door will appear and enter it.You will meet Goose[the owner. 

Grubba uses an ability to attack twice per round. He uses one of the two actions per round to fortify himself by making himself dodgy or upgrade himself. Have Yoshi as your partner. If Grubba upgrades his defense, have Yoshi use Gulp because Gulp attacks an enemy regardless of it's defense. If he upgrades his attack, have Mario use Shrink stomp to make it seem like he upgraded his attack by 1 instead of 3. If he gets dodgy, use moves that don't consume FP, such as Yoshi's Ground Pound so it won't be wasteful because dodgy means that your attacks will sometimes miss. Don't forget to appeal the audience in case you run out of FP. If this happens, have Mario use Sweet Treat.