Quick energy question
How does it work now compared to mist and does it stack? I'm just getting back into the game and hopefully will start playing more often.

The big change happened in release 2013-07-30. You can read about that (and all other changes) here:
http://wiki.spiralknights.com/Release/all
As Avenger-Of-Troy says, energy is what crystal energy used to be. You still use it to open danger rooms and special treasure rooms. Elevators are free. Crafting goes through Orbs of Alchemy. For example, in the old days you would spend 800 energy to craft a 5-star item. Now you spend 800 energy to buy 3 Eternal Orbs of Alchemy, and use those to craft. The nice thing is that you sometimes also find orbs in the Clockworks, so you get free crafting.
In the old days, players would complain about energy prices. Now players complain about the scarcity of Radiant Fire Crystals. Those are the biggest bottleneck in your progress.

Radiant Fire Crystals or "rads" are one of the most annoying aspects of the game... for most players heating up 5star. Bopp, I would like to correct you when you say, "Those are the biggest bottleneck in YOUR progress." He might be one of the minority who had all their stuff heated, and wont be that affected by the drought. Well... You still said what I didn't, so great Bopp. And thanks for the link.

Right. Maybe he already had tons of 5-star stuff heated, so the scarcity of Radiants won't affect him much. (The scarcity doesn't affect me for the same reason.) Cheers.
It's basically just how crystal energy was. I'm too lazy to get a link to the page where it says this (announcement post). Can someone go do that for me?
Also Elevators are free. New revive system (Sparks of Life) and new heat system and new alchemy system and... just check the announcement post.