I have a perfect set in mind for Hydreigon too!
A step by step guided is strongly reccomended
There is no way to get earth power without the use of gen 5 unless a friend can give it to u.
Hope I helped :)
Sadly you need BW2 to get earth power on a hydreigon. Teach hydreigon earth power with the move tutor in the town right by the volcano. Or you could get a male Garchomp with earth power and breed it with a female hydreigon. To get the Garchomp with earth power you must do the same thing above. Hope I helped!