There are 7 crystals to collect in the game. All 7 are required in the All Dungeons goal.
Crystals 5 & 6 are required to purchase the Super Bomb from the Bomb Shop to blow up the side of the Pyramid of Power to access the Pyramid Fairy.
Total number of Crystals required to open Ganon's Tower and to harm Ganon inside the Pyramid of Power can be selected from most seed generation methods.
The Crystals goal is to collect all 7 crystals and defeat Ganon. It is only available in Entrance Randomizer.