Powder Keg
The Powder Keg found in Majora's Mask is a much stronger version of the bomb. It is used mainly to clear the path to the Romani Ranch on Day One or Day Two, It's also used to blow a hole in Ikana Castle. It can only be obtained and carried when Link is in his Goron form and after he has received Powder Keg Certification from Medigoron.
Powder Keg Certification
The Powder Keg Certification allows Goron Link to use and buy Powder Kegs. After Link defeats Goht and Snowhead experiences spring again, Link will need to go back to the Goron Village and fire a Fire Arrow at the Goron Powder Keg Shop's entrance which is frozen by a huge chunk of ice. Inside, Medigoron will give Link a test to use the Powder Keg by having him take it from the Goron Village to the Goron Race Track. Once at the entrance which is blocked by a large boulder, Link will need to place the Powder Keg and let it explode on the boulder, destroying it. Once completed, Link will return to Medigoron to get the Certification which will stay on him for the rest of the game.