Recently, I've been seeing more and more players asking questions about the Energy system, so I've decided to compile some basic information and tips about it -
First and foremost: http://wiki.spiralknights.com/Energy
That will provide some great background knowledge for energy and where it can be used.
So, two big things to come out of this for newer players:
* Mist Energy regenerates over time, and you can hold up to 100 max; takes approx. 22 hours for a full recharge
* Crystal Energy is bought with either U.S. dollars OR from other players (via the Energy depot)
Many players will eventually find themselves out of ME and wonder where to go from there, so here are a few tips on how to get the most out of your energy, and how to get more (without paying a pretty penny!)
1) Do all you can on levels. Kill all the enemies, find all of the chests, explore every corner! This will get you more crowns and materials, which can be sold for even more crowns if need be. Plus, you're playing the game, and the game is fun, right?
2) Use CE revives SPARINGLY. While it may be very tempting to bring yourself back up in the heat of battle, it is not always worth it. The energy cost of revives rises rapidly (doubles on every subsequent revive), and sometimes it is just better to restart the entire run than to revive. This will net you more crowns and rewards in than end than if you used all of the energy to continue on.
Additionally, if you are with a party, use health revives as often as possible.
3) Check the Energy Market everyday! As of this writing, it is under 2000 crowns to buy 100 CE. A complete tier 1 run (provided you try and do everything) usually can net you an easy 4000 crowns, if not more. If a total Tier 1 run takes 90 CE (give or take), then you can make back all of your energy AND MORE. Of course, if you're really into it, you could try and play the market as well. ;)
4) As for crafting, if you really want to be finicky about your energy, try to always use your ME. This is best on days when you aren't planning on playing - hop on and use your ME to craft, and bam, no energy down the drain when you come back later. Using as much ME for crafting can save you the most CE in the end, though possibly at the cost of playing the game. :<
That's what I had off the top of my head - if anyone has other suggestions/comments, feel free to toss them on! Thanks!