Like that, except have a legendary trio, that is, all three legendary dragon types use three energy to power up the attacks. The trio must not have an attack that uses an energy that one of the others uses. Since there are three in a trio, and we now have nine energy types, it would totally fit.
So let's take the Reshiram, Kyurem, and Zekrom trio.
We already have a Kyurem that uses both water and psychic, so let's keep those two in there.
Reshiram of course uses fire, and Zekrom of course uses lightining.
For Reshiram and Zekrom, let us add an energy cost that is the color of that pokemon, that is Zekrom get darkness, and as for Reshiram, we can't really add colorless, because colorless doesn't have its own energy card. Kyurem is kind of gray though, so we should make Kyurem Water Psychic Metal.
Reshiram is sort of "girly" looking, so add fairy as a cost, thus making it Fire Fairy.
This leaves Grass and Fighting.
What I am thinking is Reshiram is Fire Fighting Fairy
Zekrom is Grass Lightning Darkness
Kyurem is Water Psychic Metal
Each would have an ability that does something better if one of the other two are in your bench, and does something so overpowered if all three are in your side of the field, that is one as the active, and two of them on your bench.
They could even do some super powerful attack, but the drawback is that each of the three needs to have their ultimate attack powered up, thus making you have to run a deck that uses all 9 energy types. If you don't have the other two's ultimate attack powered up, Zekrom's ultimate attack is just like any other attack. So let's say it does uh, 100 damage? If all 3 were powered up, maybe it could do 200 damage and recycles all energy back from the discard pile to the field, or something overpowered like that?
So what I would like to see are a trio of dragon types, hopefully a legendary dragon trio, where one card becomes better if the other two are on your side of the field, and each of them has an attack cost that requires 3 different energy types, where no two have the same energy type as a cost, and in order to maximize the power of the attack, all 9 energy types are required. I'm not saying that each individual card has to suck. The attack that requires 3 energy types has to be a good attack, but will become overpowered if the other 2 in the trio are on your bench, and becomes even more powerful if their respective attacks are powered up with energy.
Doesn't anyone here feel good if they completely wipe the opponent's side of the field by pulling off an attack that is super hard to set up?