The Erebus Mod 1.7.10, 1.7.2 focuses on adding a whole new dimension to Minecraft, with many new creatures to slay, things to create and lands to explore. Other things, such as an in-depth magic system and many dungeons are planned as well.

This dimension is designed to provide full survivability, giving you the ability to start from scratch there if you so desire. This is, however, not recommended, as mobs are a lot tougher. The mobs are rather diverse in their AI, and even the passive mobs are not completely harmless.
This mod plays well with almost all other mods, and is designed for compatibility with both magic and tech mods. You can turn on a variety of ores commonly used in mods, such as Copper, Tin, Silver, Lead and Aluminum, so you never have to leave!