Dialga Lv.X really isn't a great card. Although the Poke Power might look like it is good, you still have that chance of your turn ending. And doing 80 for four and not being able to use that attack during your next turn either isn't a great as well. So, he is flippy and doesn't have good attack effects. On the other hand, Special Metal Energy does benefit Dialga...
And before anyone posts this idea, Shiftry RR doesn't work with Dialga Lv.X.