The core of the mod is the Essences. The Essences are really powerful stuff, and you can use that to craft some powerful tools, weapons and armors. Better than Diamond! Currently, there are 3 Essences (Electric Essence, Nether Essence and Ender Essence), but more will come in the future. The mod is under development. You craft Essences using a bunch of materials related to the theme of the essence. You'll need a lot of stuff to make Essences, so automating anything possible is important. Detailed description of the mod is in the Minecraft Forums thread.
In version 0.3.2+ of this mod, there are new mobs added. 0.3.2 added the Charged mobs, and 0.3.3 added the Nether mobs. As of 0.3.3, this mod includes 10 mobs, with 2 bosses, which are the Charged Wither and the Inferno Beast. To kill these bosses, you can't just fight without skill and strategy, or they'll most likely kill you and you can't do much damage to them. They can only be killed with good equipment, skill, and strategy. It is highly recommended to practice the boss battles in another world before killing them in your survival world, because if you don't have the right strategy, it is almost impossible to get these bosses out of your world. All mobs, except the Charged Wither, do spawn naturally, so watch out for them!
Feel free to use the mod in any modpacks. You are allowed to use it, you do not need to ask for permission.
Also, the lightning and fireballs are not normal lightning and fireballs. They are more powerful than vanilla lightning and fireballs.