User blog comment:AP Sejuani/Vortelle, the Black Hole/@comment-10958553-20140919165106

So the purpose of energy is to make a champion be limited in his combo, with low cooldowns, but be able to keep building up the resource quick enough to hit off another full combo in 20 seconds.

The purpose of mana is to have clearly visible resource that can be tracked as it goes down in lane. Enemies with low mana are more vulnerable, where as enemies with high mana, have their skills available.

So you are combining those? so that she can eventually run out in lane, but also be restricted in how large her combos are?

Looking over her cooldowns, i think that surge needs to have the 75 cost on both activations. Thats the only wat to make the energy cost make sense. I do like that it only costs energy though, so it shoudl  always end up being available.