Mountain Climbing Permit
From the Super Mario Wiki
When Mario and Huey go to Daffodil Peak, the gatekeeper, who is later revealed to be the Mountain Sage, tells them that they have to speak to the park ranger to get a permit. When Mario arrives at the park ranger's cabin, the park ranger tells him that the cabin had been vandalized, and that he is too depressed to give Mario a permit. After Mario fixes up the cabin, the park ranger gives Mario a free Mountain Climbing Permit that had been kept inside of a safe. Once Mario shows the Permit to the gatekeeper, he is allowed to climb the mountain.
According to the park ranger, Mountain Climbing Permits are usually expensive.