The Bombos Medallion is found at an ancient tablet on a cliff overlooking the Desert Area. Ordinarily this cliff is inaccessible in the Light World, and the player will need to head west from the Swamp Palace area in the Dark World, pass the hammer pegs, and use the Mirror to warp to this ledge. Using Clips, this medallion can be accessed from the Light World.
In order to read the tablet and receive the Medallion, Link will also need a Level 2 sword or greater (Master Sword, Tempered Sword, or Golden Sword) and the Book of Mudora.
Even with the Medallion in Link's inventory, it cannot be used if Link is swordless.
Using the Bombos Medallion creates a huge onscreen explosion at the cost of 32 MP (4 uses with normal magic, 8 with the 1/2 magic upgrade). This will kill all normal enemies on screen immediately, making it more powerful than the other medallions. Unlike the other two medallions though, Bombos is not required to open any dungeons and is therefore skipped in all non-100% speedruns.
Against Kholdstare, Bombos can be used to melt the first phase ice shield. Bombos has no use against bosses other than this.