The type and base power of Hidden Power is randomly calculated whenever a Pokémon enters a dungeon, and does not change between floors. The type is selected among each of the 17 types with roughly equal probability (the game chooses from the 18 types, including the ???-type, choosing again if the ???-type is chosen; if this is done 100 times consecutively, Hidden Power will be of the Fire-type). The base power of the move is chosen among the following values with equal probability: 2, 4, 6, 7, 8, 9, 10, 13, 15, and 17

sorry its copy and pasted didnt relly understand it (from bulbapedia)